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 $216.34   6.202%   $229.7574   $229.76   $229.75   $229.80  
  Purchase #2 $45.55   7.375%   $48.9093   $48.91   $48.90   $48.90  
  Purchase #3 $195.80   4.138%   $203.9022   $203.90   $203.90   $203.90  
  Purchase #4 $151.29   7.259%   $162.2721   $162.27   $162.25   $162.30  
  Purchase #5 $90.75   5.776%   $95.9917   $95.99   $96.00   $96.00  
  Purchase #6 $34.34   4.235%   $35.7943   $35.79   $35.80   $35.80  
  Purchase #7 $142.86   5.204%   $150.2944   $150.29   $150.30   $150.30  
  7 purchase totals = $876.93       $926.9214   $926.91   $926.90   $927.00