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 $216.92   12.722%   $244.5166   $244.52   $244.50   $244.50  
  Purchase #2 $24.77   11.180%   $27.5393   $27.54   $27.55   $27.50  
  Purchase #3 $150.46   9.545%   $164.8214   $164.82   $164.80   $164.80  
  Purchase #4 $104.94   8.713%   $114.0834   $114.08   $114.10   $114.10  
  Purchase #5 $33.54   8.430%   $36.3674   $36.37   $36.35   $36.40  
  Purchase #6 $78.45   6.367%   $83.4449   $83.44   $83.45   $83.40  
  Purchase #7 $181.87   8.330%   $197.0198   $197.02   $197.00   $197.00  
  7 purchase totals = $790.95       $867.7928   $867.79   $867.75   $867.70