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 $54.27   13.533%   $61.6144   $61.61   $61.60   $61.60  
  Purchase #2 $148.97   11.376%   $165.9168   $165.92   $165.90   $165.90  
  Purchase #3 $227.88   10.253%   $251.2445   $251.24   $251.25   $251.20  
  Purchase #4 $182.42   12.823%   $205.8117   $205.81   $205.80   $205.80  
  Purchase #5 $123.54   9.576%   $135.3702   $135.37   $135.35   $135.40  
  Purchase #6 $8.93   12.144%   $10.0145   $10.01   $10.00   $10.00  
  Purchase #7 $115.51   7.785%   $124.5025   $124.50   $124.50   $124.50  
  7 purchase totals = $861.52       $954.4746   $954.46   $954.40   $954.40