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 $68.77   6.678%   $73.3625   $73.36   $73.35   $73.40  
  Purchase #2 $210.45   8.650%   $228.6539   $228.65   $228.65   $228.70  
  Purchase #3 $178.76   8.408%   $193.7901   $193.79   $193.80   $193.80  
  Purchase #4 $133.84   3.266%   $138.2112   $138.21   $138.20   $138.20  
  Purchase #5 $51.89   8.829%   $56.4714   $56.47   $56.45   $56.50  
  Purchase #6 $47.82   9.700%   $52.4585   $52.46   $52.45   $52.50  
  Purchase #7 $19.75   6.253%   $20.985   $20.99   $21.00   $21.00  
  7 purchase totals = $711.28       $763.9326   $763.93   $763.90   $764.10