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 $68.70   5.354%   $72.3782   $72.38   $72.40   $72.40  
  Purchase #2 $210.74   6.650%   $224.7542   $224.75   $224.75   $224.80  
  Purchase #3 $179.48   11.716%   $200.5079   $200.51   $200.50   $200.50  
  Purchase #4 $239.33   7.359%   $256.9423   $256.94   $256.95   $256.90  
  Purchase #5 $150.47   13.241%   $170.3937   $170.39   $170.40   $170.40  
  Purchase #6 $24.53   6.847%   $26.2096   $26.21   $26.20   $26.20  
  Purchase #7 $229.80   8.794%   $250.0086   $250.01   $250.00   $250.00  
  7 purchase totals = $1,103.05       $1,201.1945   $1,201.19   $1,201.20   $1,201.20