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 $173.36   12.246%   $194.5897   $194.59   $194.60   $194.60  
  Purchase #2 $226.46   3.775%   $235.0089   $235.01   $235.00   $235.00  
  Purchase #3 $17.34   3.361%   $17.9228   $17.92   $17.90   $17.90  
  Purchase #4 $65.81   9.641%   $72.1547   $72.15   $72.15   $72.20  
  Purchase #5 $23.88   12.753%   $26.9254   $26.93   $26.95   $26.90  
  Purchase #6 $43.72   9.788%   $47.9993   $48.00   $48.00   $48.00  
  Purchase #7 $149.81   4.165%   $156.0496   $156.05   $156.05   $156.00  
  7 purchase totals = $700.38       $750.6504   $750.65   $750.65   $750.60