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 $13.52   6.171%   $14.3543   $14.35   $14.35   $14.40  
  Purchase #2 $95.83   11.216%   $106.5783   $106.58   $106.60   $106.60  
  Purchase #3 $39.55   11.549%   $44.1176   $44.12   $44.10   $44.10  
  Purchase #4 $68.61   12.139%   $76.9386   $76.94   $76.95   $76.90  
  Purchase #5 $236.33   8.871%   $257.2948   $257.29   $257.30   $257.30  
  Purchase #6 $75.78   7.403%   $81.39   $81.39   $81.40   $81.40  
  Purchase #7 $221.82   12.675%   $249.9357   $249.94   $249.95   $249.90  
  7 purchase totals = $751.44       $830.6093   $830.61   $830.65   $830.60