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 $66.61   13.310%   $75.4758   $75.48   $75.50   $75.50  
  Purchase #2 $98.98   13.485%   $112.3275   $112.33   $112.35   $112.30  
  Purchase #3 $70.83   3.849%   $73.5562   $73.56   $73.55   $73.60  
  Purchase #4 $81.60   11.606%   $91.0705   $91.07   $91.05   $91.10  
  Purchase #5 $204.72   9.872%   $224.93   $224.93   $224.95   $224.90  
  Purchase #6 $170.41   8.618%   $185.0959   $185.10   $185.10   $185.10  
  Purchase #7 $174.52   7.427%   $187.4816   $187.48   $187.50   $187.50  
  7 purchase totals = $867.67       $949.9375   $949.95   $950.00   $950.00