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 $247.94   6.104%   $263.0743   $263.07   $263.05   $263.10  
  Purchase #2 $206.97   13.870%   $235.6767   $235.68   $235.70   $235.70  
  Purchase #3 $73.86   12.418%   $83.0319   $83.03   $83.05   $83.00  
  Purchase #4 $94.62   7.830%   $102.0287   $102.03   $102.05   $102.00  
  Purchase #5 $194.31   3.583%   $201.2721   $201.27   $201.25   $201.30  
  Purchase #6 $5.82   5.574%   $6.1444   $6.14   $6.15   $6.10  
  Purchase #7 $210.97   7.434%   $226.6535   $226.65   $226.65   $226.70  
  7 purchase totals = $1,034.49       $1,117.8816   $1,117.87   $1,117.90   $1,117.90