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 $178.59   10.624%   $197.5634   $197.56   $197.55   $197.60  
  Purchase #2 $138.51   13.302%   $156.9346   $156.93   $156.95   $156.90  
  Purchase #3 $138.99   6.668%   $148.2579   $148.26   $148.25   $148.30  
  Purchase #4 $116.27   6.807%   $124.1845   $124.18   $124.20   $124.20  
  Purchase #5 $212.47   5.148%   $223.408   $223.41   $223.40   $223.40  
  Purchase #6 $146.99   12.679%   $165.6269   $165.63   $165.65   $165.60  
  Purchase #7 $232.86   7.185%   $249.591   $249.59   $249.60   $249.60  
  7 purchase totals = $1,164.68       $1,265.5663   $1,265.56   $1,265.60   $1,265.60