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 $53.65   4.289%   $55.951   $55.95   $55.95   $56.00  
  Purchase #2 $70.45   7.110%   $75.459   $75.46   $75.45   $75.50  
  Purchase #3 $151.91   12.580%   $171.0203   $171.02   $171.00   $171.00  
  Purchase #4 $158.87   12.841%   $179.2705   $179.27   $179.25   $179.30  
  Purchase #5 $196.75   9.514%   $215.4688   $215.47   $215.45   $215.50  
  Purchase #6 $157.45   11.612%   $175.7331   $175.73   $175.75   $175.70  
  Purchase #7 $125.97   7.682%   $135.647   $135.65   $135.65   $135.60  
  7 purchase totals = $915.05       $1,008.5497   $1,008.55   $1,008.50   $1,008.60