Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $157.84   12.621%   $177.761   $177.76   $177.75   $177.80  
  Purchase #2 $190.63   4.215%   $198.6651   $198.67   $198.65   $198.70  
  Purchase #3 $153.42   10.551%   $169.6073   $169.61   $169.60   $169.60  
  Purchase #4 $178.74   9.495%   $195.7114   $195.71   $195.70   $195.70  
  Purchase #5 $190.55   10.723%   $210.9827   $210.98   $211.00   $211.00  
  Purchase #6 $215.55   11.742%   $240.8599   $240.86   $240.85   $240.90  
  Purchase #7 $165.42   6.787%   $176.6471   $176.65   $176.65   $176.60  
  7 purchase totals = $1,252.15       $1,370.2345   $1,370.24   $1,370.20   $1,370.30