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 $210.82   10.206%   $232.3363   $232.34   $232.35   $232.30  
  Purchase #2 $201.63   4.731%   $211.1691   $211.17   $211.15   $211.20  
  Purchase #3 $79.61   9.557%   $87.2183   $87.22   $87.20   $87.20  
  Purchase #4 $43.84   8.679%   $47.6449   $47.64   $47.65   $47.60  
  Purchase #5 $241.50   3.202%   $249.2328   $249.23   $249.25   $249.20  
  Purchase #6 $13.94   3.440%   $14.4195   $14.42   $14.40   $14.40  
  Purchase #7 $131.30   9.155%   $143.3205   $143.32   $143.30   $143.30  
  7 purchase totals = $922.64       $985.3414   $985.34   $985.30   $985.20