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 $44.53   13.617%   $50.5937   $50.59   $50.60   $50.60  
  Purchase #2 $244.53   4.828%   $256.3359   $256.34   $256.35   $256.30  
  Purchase #3 $117.84   11.847%   $131.8005   $131.80   $131.80   $131.80  
  Purchase #4 $219.97   8.231%   $238.0757   $238.08   $238.10   $238.10  
  Purchase #5 $216.55   12.271%   $243.1229   $243.12   $243.10   $243.10  
  Purchase #6 $212.48   6.871%   $227.0795   $227.08   $227.10   $227.10  
  Purchase #7 $115.83   6.758%   $123.6578   $123.66   $123.65   $123.70  
  7 purchase totals = $1,171.73       $1,270.6660   $1,270.67   $1,270.70   $1,270.70