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 $51.66   4.544%   $54.0074   $54.01   $54.00   $54.00  
  Purchase #2 $16.36   11.509%   $18.2429   $18.24   $18.25   $18.20  
  Purchase #3 $103.64   11.507%   $115.5659   $115.57   $115.55   $115.60  
  Purchase #4 $23.79   6.528%   $25.343   $25.34   $25.35   $25.30  
  Purchase #5 $167.25   9.111%   $182.4881   $182.49   $182.50   $182.50  
  Purchase #6 $226.47   8.170%   $244.9726   $244.97   $244.95   $245.00  
  Purchase #7 $137.85   10.388%   $152.1699   $152.17   $152.15   $152.20  
  7 purchase totals = $727.02       $792.7898   $792.79   $792.75   $792.80