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 $179.47   10.534%   $198.3754   $198.38   $198.40   $198.40  
  Purchase #2 $144.38   8.145%   $156.1398   $156.14   $156.15   $156.10  
  Purchase #3 $185.56   8.855%   $201.9913   $201.99   $202.00   $202.00  
  Purchase #4 $94.32   10.234%   $103.9727   $103.97   $103.95   $104.00  
  Purchase #5 $165.35   8.478%   $179.3684   $179.37   $179.35   $179.40  
  Purchase #6 $250.76   3.760%   $260.1886   $260.19   $260.20   $260.20  
  Purchase #7 $84.27   12.626%   $94.9099   $94.91   $94.90   $94.90  
  7 purchase totals = $1,104.11       $1,194.9461   $1,194.95   $1,194.95   $1,195.00