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 $112.66   12.122%   $126.3166   $126.32   $126.30   $126.30  
  Purchase #2 $58.43   13.181%   $66.1317   $66.13   $66.15   $66.10  
  Purchase #3 $142.96   12.215%   $160.4226   $160.42   $160.40   $160.40  
  Purchase #4 $171.47   13.123%   $193.972   $193.97   $193.95   $194.00  
  Purchase #5 $38.80   13.153%   $43.9034   $43.90   $43.90   $43.90  
  Purchase #6 $163.91   6.241%   $174.1396   $174.14   $174.15   $174.10  
  Purchase #7 $233.48   13.275%   $264.4745   $264.47   $264.45   $264.50  
  7 purchase totals = $921.71       $1,029.3604   $1,029.35   $1,029.30   $1,029.30