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 $219.54   13.793%   $249.8212   $249.82   $249.80   $249.80  
  Purchase #2 $13.89   5.651%   $14.6749   $14.67   $14.65   $14.70  
  Purchase #3 $62.90   8.275%   $68.105   $68.11   $68.10   $68.10  
  Purchase #4 $101.33   13.823%   $115.3368   $115.34   $115.35   $115.30  
  Purchase #5 $137.75   13.626%   $156.5198   $156.52   $156.50   $156.50  
  Purchase #6 $163.91   10.630%   $181.3336   $181.33   $181.35   $181.30  
  Purchase #7 $178.56   12.254%   $200.4407   $200.44   $200.45   $200.40  
  7 purchase totals = $877.88       $986.2320   $986.23   $986.20   $986.10