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 $56.28   9.440%   $61.5928   $61.59   $61.60   $61.60  
  Purchase #2 $142.42   6.112%   $151.1247   $151.12   $151.10   $151.10  
  Purchase #3 $160.94   9.855%   $176.8006   $176.80   $176.80   $176.80  
  Purchase #4 $37.93   10.522%   $41.921   $41.92   $41.90   $41.90  
  Purchase #5 $219.78   9.634%   $240.9536   $240.95   $240.95   $241.00  
  Purchase #6 $15.68   4.695%   $16.4162   $16.42   $16.40   $16.40  
  Purchase #7 $242.87   7.128%   $260.1818   $260.18   $260.20   $260.20  
  7 purchase totals = $875.90       $948.9907   $948.98   $948.95   $949.00