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 $241.82   6.712%   $258.051   $258.05   $258.05   $258.10  
  Purchase #2 $187.73   12.380%   $210.971   $210.97   $210.95   $211.00  
  Purchase #3 $230.99   13.831%   $262.9382   $262.94   $262.95   $262.90  
  Purchase #4 $154.41   7.666%   $166.2471   $166.25   $166.25   $166.20  
  Purchase #5 $240.43   13.513%   $272.9193   $272.92   $272.90   $272.90  
  Purchase #6 $157.29   7.872%   $169.6719   $169.67   $169.65   $169.70  
  Purchase #7 $218.38   6.291%   $232.1183   $232.12   $232.10   $232.10  
  7 purchase totals = $1,431.05       $1,572.9168   $1,572.92   $1,572.85   $1,572.90