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 $60.78   5.269%   $63.9825   $63.98   $64.00   $64.00  
  Purchase #2 $200.42   13.467%   $227.4106   $227.41   $227.40   $227.40  
  Purchase #3 $7.75   12.792%   $8.7414   $8.74   $8.75   $8.70  
  Purchase #4 $246.39   3.209%   $254.2967   $254.30   $254.30   $254.30  
  Purchase #5 $54.88   4.234%   $57.2036   $57.20   $57.20   $57.20  
  Purchase #6 $192.38   9.459%   $210.5772   $210.58   $210.60   $210.60  
  Purchase #7 $139.33   9.795%   $152.9774   $152.98   $153.00   $153.00  
  7 purchase totals = $901.93       $975.1894   $975.19   $975.25   $975.20