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 $84.83   10.344%   $93.6048   $93.60   $93.60   $93.60  
  Purchase #2 $171.35   7.289%   $183.8397   $183.84   $183.85   $183.80  
  Purchase #3 $44.37   5.306%   $46.7243   $46.72   $46.70   $46.70  
  Purchase #4 $183.99   4.460%   $192.196   $192.20   $192.20   $192.20  
  Purchase #5 $241.46   12.190%   $270.894   $270.89   $270.90   $270.90  
  Purchase #6 $241.69   4.366%   $252.2422   $252.24   $252.25   $252.20  
  Purchase #7 $172.87   9.324%   $188.9884   $188.99   $189.00   $189.00  
  7 purchase totals = $1,140.56       $1,228.4894   $1,228.48   $1,228.50   $1,228.40