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 $83.42   13.763%   $94.9011   $94.90   $94.90   $94.90  
  Purchase #2 $25.65   7.341%   $27.533   $27.53   $27.55   $27.50  
  Purchase #3 $120.98   10.595%   $133.7978   $133.80   $133.80   $133.80  
  Purchase #4 $153.73   4.264%   $160.285   $160.29   $160.30   $160.30  
  Purchase #5 $104.83   6.198%   $111.3274   $111.33   $111.35   $111.30  
  Purchase #6 $126.72   12.869%   $143.0276   $143.03   $143.05   $143.00  
  Purchase #7 $91.62   6.392%   $97.4764   $97.48   $97.50   $97.50  
  7 purchase totals = $706.95       $768.3483   $768.36   $768.45   $768.30