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 $213.53   5.867%   $226.0578   $226.06   $226.05   $226.10  
  Purchase #2 $202.39   6.742%   $216.0351   $216.04   $216.05   $216.00  
  Purchase #3 $58.64   9.255%   $64.0671   $64.07   $64.05   $64.10  
  Purchase #4 $211.78   5.134%   $222.6528   $222.65   $222.65   $222.70  
  Purchase #5 $87.85   8.504%   $95.3208   $95.32   $95.30   $95.30  
  Purchase #6 $17.44   12.451%   $19.6115   $19.61   $19.60   $19.60  
  Purchase #7 $204.82   12.249%   $229.9084   $229.91   $229.90   $229.90  
  7 purchase totals = $996.45       $1,073.6535   $1,073.66   $1,073.60   $1,073.70