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 $61.93   3.816%   $64.2932   $64.29   $64.30   $64.30  
  Purchase #2 $246.89   4.748%   $258.6123   $258.61   $258.60   $258.60  
  Purchase #3 $16.80   9.716%   $18.4323   $18.43   $18.45   $18.40  
  Purchase #4 $10.96   3.585%   $11.3529   $11.35   $11.35   $11.40  
  Purchase #5 $205.36   10.797%   $227.5327   $227.53   $227.55   $227.50  
  Purchase #6 $242.26   7.240%   $259.7996   $259.80   $259.80   $259.80  
  Purchase #7 $183.75   7.718%   $197.9318   $197.93   $197.95   $197.90  
  7 purchase totals = $967.95       $1,037.9548   $1,037.94   $1,038.00   $1,037.90