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 $61.47   12.211%   $68.9761   $68.98   $69.00   $69.00  
  Purchase #2 $39.32   8.437%   $42.6374   $42.64   $42.65   $42.60  
  Purchase #3 $51.53   4.297%   $53.7442   $53.74   $53.75   $53.70  
  Purchase #4 $25.76   9.289%   $28.1528   $28.15   $28.15   $28.20  
  Purchase #5 $53.66   4.662%   $56.1616   $56.16   $56.15   $56.20  
  Purchase #6 $232.68   3.148%   $240.0048   $240.00   $240.00   $240.00  
  Purchase #7 $88.28   9.866%   $96.9897   $96.99   $97.00   $97.00  
  7 purchase totals = $552.70       $586.6666   $586.66   $586.70   $586.70