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 $213.56   13.292%   $241.9464   $241.95   $241.95   $241.90  
  Purchase #2 $102.86   4.554%   $107.5442   $107.54   $107.55   $107.50  
  Purchase #3 $189.85   6.689%   $202.5491   $202.55   $202.55   $202.50  
  Purchase #4 $174.79   8.612%   $189.8429   $189.84   $189.85   $189.80  
  Purchase #5 $164.59   7.166%   $176.3845   $176.38   $176.40   $176.40  
  Purchase #6 $235.50   12.315%   $264.5018   $264.50   $264.50   $264.50  
  Purchase #7 $147.35   12.484%   $165.7452   $165.75   $165.75   $165.70  
  7 purchase totals = $1,228.50       $1,348.5141   $1,348.51   $1,348.55   $1,348.30