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 $62.53   13.644%   $71.0616   $71.06   $71.05   $71.10  
  Purchase #2 $173.33   4.226%   $180.6549   $180.65   $180.65   $180.70  
  Purchase #3 $43.96   9.805%   $48.2703   $48.27   $48.25   $48.30  
  Purchase #4 $82.56   5.743%   $87.3014   $87.30   $87.30   $87.30  
  Purchase #5 $145.77   12.245%   $163.6195   $163.62   $163.60   $163.60  
  Purchase #6 $12.92   4.350%   $13.482   $13.48   $13.50   $13.50  
  Purchase #7 $26.68   6.616%   $28.4451   $28.45   $28.45   $28.40  
  7 purchase totals = $547.75       $592.8348   $592.83   $592.80   $592.90