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 $54.93   11.826%   $61.426   $61.43   $61.45   $61.40  
  Purchase #2 $126.94   4.569%   $132.7399   $132.74   $132.75   $132.70  
  Purchase #3 $59.74   7.437%   $64.1829   $64.18   $64.20   $64.20  
  Purchase #4 $54.85   10.434%   $60.573   $60.57   $60.55   $60.60  
  Purchase #5 $69.72   7.748%   $75.1219   $75.12   $75.10   $75.10  
  Purchase #6 $17.32   13.458%   $19.6509   $19.65   $19.65   $19.70  
  Purchase #7 $241.40   4.714%   $252.7796   $252.78   $252.80   $252.80  
  7 purchase totals = $624.90       $666.4742   $666.47   $666.50   $666.50