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 $239.79   8.525%   $260.2321   $260.23   $260.25   $260.20  
  Purchase #2 $111.73   8.625%   $121.3667   $121.37   $121.35   $121.40  
  Purchase #3 $118.82   12.336%   $133.4776   $133.48   $133.50   $133.50  
  Purchase #4 $245.73   6.786%   $262.4052   $262.41   $262.40   $262.40  
  Purchase #5 $166.41   7.614%   $179.0805   $179.08   $179.10   $179.10  
  Purchase #6 $187.45   13.590%   $212.9245   $212.92   $212.90   $212.90  
  Purchase #7 $159.99   11.562%   $178.488   $178.49   $178.50   $178.50  
  7 purchase totals = $1,229.92       $1,347.9746   $1,347.98   $1,348.00   $1,348.00