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 $69.94   13.638%   $79.4784   $79.48   $79.50   $79.50  
  Purchase #2 $147.78   9.542%   $161.8812   $161.88   $161.90   $161.90  
  Purchase #3 $23.51   9.725%   $25.7963   $25.80   $25.80   $25.80  
  Purchase #4 $51.35   12.740%   $57.892   $57.89   $57.90   $57.90  
  Purchase #5 $93.75   13.489%   $106.3959   $106.40   $106.40   $106.40  
  Purchase #6 $158.89   10.468%   $175.5226   $175.52   $175.50   $175.50  
  Purchase #7 $111.80   11.841%   $125.0382   $125.04   $125.05   $125.00  
  7 purchase totals = $657.02       $732.0046   $732.01   $732.05   $732.00