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 $40.71   7.267%   $43.6684   $43.67   $43.65   $43.70  
  Purchase #2 $244.99   13.315%   $277.6104   $277.61   $277.60   $277.60  
  Purchase #3 $126.50   5.705%   $133.7168   $133.72   $133.70   $133.70  
  Purchase #4 $191.49   6.137%   $203.2417   $203.24   $203.25   $203.20  
  Purchase #5 $207.98   13.682%   $236.4358   $236.44   $236.45   $236.40  
  Purchase #6 $35.98   4.786%   $37.702   $37.70   $37.70   $37.70  
  Purchase #7 $145.51   7.163%   $155.9329   $155.93   $155.95   $155.90  
  7 purchase totals = $993.16       $1,088.3080   $1,088.31   $1,088.30   $1,088.20