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 $176.74   12.435%   $198.7176   $198.72   $198.70   $198.70  
  Purchase #2 $169.85   3.357%   $175.5519   $175.55   $175.55   $175.60  
  Purchase #3 $187.48   6.518%   $199.6999   $199.70   $199.70   $199.70  
  Purchase #4 $119.82   11.335%   $133.4016   $133.40   $133.40   $133.40  
  Purchase #5 $40.87   7.873%   $44.0877   $44.09   $44.10   $44.10  
  Purchase #6 $199.82   5.584%   $210.9779   $210.98   $211.00   $211.00  
  Purchase #7 $67.66   8.317%   $73.2873   $73.29   $73.30   $73.30  
  7 purchase totals = $962.24       $1,035.7239   $1,035.73   $1,035.75   $1,035.80