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 $47.41   11.224%   $52.7313   $52.73   $52.75   $52.70  
  Purchase #2 $212.49   9.524%   $232.7275   $232.73   $232.75   $232.70  
  Purchase #3 $5.45   3.585%   $5.6454   $5.65   $5.65   $5.60  
  Purchase #4 $191.70   5.656%   $202.5426   $202.54   $202.55   $202.50  
  Purchase #5 $209.75   10.812%   $232.4282   $232.43   $232.45   $232.40  
  Purchase #6 $5.90   3.791%   $6.1237   $6.12   $6.10   $6.10  
  Purchase #7 $112.76   10.816%   $124.9561   $124.96   $124.95   $125.00  
  7 purchase totals = $785.46       $857.1548   $857.16   $857.20   $857.00