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 $139.87   8.408%   $151.6303   $151.63   $151.65   $151.60  
  Purchase #2 $221.61   11.306%   $246.6652   $246.67   $246.65   $246.70  
  Purchase #3 $59.52   11.168%   $66.1672   $66.17   $66.15   $66.20  
  Purchase #4 $35.37   8.210%   $38.2739   $38.27   $38.25   $38.30  
  Purchase #5 $14.25   5.490%   $15.0323   $15.03   $15.05   $15.00  
  Purchase #6 $27.27   7.572%   $29.3349   $29.33   $29.35   $29.30  
  Purchase #7 $157.89   8.705%   $171.6343   $171.63   $171.65   $171.60  
  7 purchase totals = $655.78       $718.7381   $718.73   $718.75   $718.70