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 $113.72   4.266%   $118.5713   $118.57   $118.55   $118.60  
  Purchase #2 $222.93   5.513%   $235.2201   $235.22   $235.20   $235.20  
  Purchase #3 $139.27   8.364%   $150.9185   $150.92   $150.90   $150.90  
  Purchase #4 $201.63   6.587%   $214.9114   $214.91   $214.90   $214.90  
  Purchase #5 $25.49   9.492%   $27.9095   $27.91   $27.90   $27.90  
  Purchase #6 $249.51   13.471%   $283.1215   $283.12   $283.10   $283.10  
  Purchase #7 $62.68   4.738%   $65.6498   $65.65   $65.65   $65.60  
  7 purchase totals = $1,015.23       $1,096.3021   $1,096.30   $1,096.20   $1,096.20