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 $44.38   5.171%   $46.6749   $46.67   $46.65   $46.70  
  Purchase #2 $21.33   9.109%   $23.2729   $23.27   $23.25   $23.30  
  Purchase #3 $210.26   6.248%   $223.397   $223.40   $223.40   $223.40  
  Purchase #4 $142.82   13.433%   $162.005   $162.01   $162.00   $162.00  
  Purchase #5 $59.79   5.331%   $62.9774   $62.98   $63.00   $63.00  
  Purchase #6 $137.29   3.394%   $141.9496   $141.95   $141.95   $141.90  
  Purchase #7 $250.91   6.484%   $267.179   $267.18   $267.20   $267.20  
  7 purchase totals = $866.78       $927.4558   $927.46   $927.45   $927.50