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 $189.33   9.421%   $207.1668   $207.17   $207.15   $207.20  
  Purchase #2 $157.30   11.420%   $175.2637   $175.26   $175.25   $175.30  
  Purchase #3 $37.87   8.271%   $41.0022   $41.00   $41.00   $41.00  
  Purchase #4 $151.86   10.462%   $167.7476   $167.75   $167.75   $167.70  
  Purchase #5 $194.74   7.498%   $209.3416   $209.34   $209.35   $209.30  
  Purchase #6 $235.97   13.489%   $267.8   $267.80   $267.80   $267.80  
  Purchase #7 $188.26   7.310%   $202.0218   $202.02   $202.00   $202.00  
  7 purchase totals = $1,155.33       $1,270.3437   $1,270.34   $1,270.30   $1,270.30