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 $58.33   5.556%   $61.5708   $61.57   $61.55   $61.60  
  Purchase #2 $45.52   12.112%   $51.0334   $51.03   $51.05   $51.00  
  Purchase #3 $25.96   12.846%   $29.2948   $29.29   $29.30   $29.30  
  Purchase #4 $57.96   12.136%   $64.994   $64.99   $65.00   $65.00  
  Purchase #5 $6.60   12.377%   $7.4169   $7.42   $7.40   $7.40  
  Purchase #6 $212.98   13.801%   $242.3734   $242.37   $242.35   $242.40  
  Purchase #7 $217.49   13.330%   $246.4814   $246.48   $246.50   $246.50  
  7 purchase totals = $624.84       $703.1647   $703.15   $703.15   $703.20