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 $66.62   12.572%   $74.9955   $75.00   $75.00   $75.00  
  Purchase #2 $162.35   3.739%   $168.4203   $168.42   $168.40   $168.40  
  Purchase #3 $70.98   5.136%   $74.6255   $74.63   $74.65   $74.60  
  Purchase #4 $238.76   8.685%   $259.4963   $259.50   $259.50   $259.50  
  Purchase #5 $173.60   4.767%   $181.8755   $181.88   $181.90   $181.90  
  Purchase #6 $121.72   6.764%   $129.9531   $129.95   $129.95   $130.00  
  Purchase #7 $35.84   4.782%   $37.5539   $37.55   $37.55   $37.60  
  7 purchase totals = $869.87       $926.9201   $926.93   $926.95   $927.00