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 $61.88   5.232%   $65.1176   $65.12   $65.10   $65.10  
  Purchase #2 $92.36   3.301%   $95.4088   $95.41   $95.40   $95.40  
  Purchase #3 $69.59   3.121%   $71.7619   $71.76   $71.75   $71.80  
  Purchase #4 $244.63   8.199%   $264.6872   $264.69   $264.70   $264.70  
  Purchase #5 $54.68   12.199%   $61.3504   $61.35   $61.35   $61.40  
  Purchase #6 $232.48   9.198%   $253.8635   $253.86   $253.85   $253.90  
  Purchase #7 $138.73   8.537%   $150.5734   $150.57   $150.55   $150.60  
  7 purchase totals = $894.35       $962.7628   $962.76   $962.70   $962.90