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 $52.41   12.505%   $58.9639   $58.96   $58.95   $59.00  
  Purchase #2 $168.26   9.317%   $183.9368   $183.94   $183.95   $183.90  
  Purchase #3 $98.28   3.239%   $101.4633   $101.46   $101.45   $101.50  
  Purchase #4 $117.80   12.779%   $132.8537   $132.85   $132.85   $132.90  
  Purchase #5 $212.58   4.687%   $222.5436   $222.54   $222.55   $222.50  
  Purchase #6 $103.57   5.867%   $109.6465   $109.65   $109.65   $109.60  
  Purchase #7 $204.50   11.344%   $227.6985   $227.70   $227.70   $227.70  
  7 purchase totals = $957.40       $1,037.1063   $1,037.10   $1,037.10   $1,037.10