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 $84.27   8.120%   $91.1127   $91.11   $91.10   $91.10  
  Purchase #2 $205.66   13.353%   $233.1218   $233.12   $233.10   $233.10  
  Purchase #3 $120.79   7.195%   $129.4808   $129.48   $129.50   $129.50  
  Purchase #4 $95.51   5.602%   $100.8605   $100.86   $100.85   $100.90  
  Purchase #5 $151.74   4.314%   $158.2861   $158.29   $158.30   $158.30  
  Purchase #6 $68.52   9.371%   $74.941   $74.94   $74.95   $74.90  
  Purchase #7 $156.53   4.775%   $164.0043   $164.00   $164.00   $164.00  
  7 purchase totals = $883.02       $951.8072   $951.80   $951.80   $951.80