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 $59.89   4.691%   $62.6994   $62.70   $62.70   $62.70  
  Purchase #2 $214.57   6.820%   $229.2037   $229.20   $229.20   $229.20  
  Purchase #3 $150.41   11.446%   $167.6259   $167.63   $167.65   $167.60  
  Purchase #4 $41.44   3.751%   $42.9944   $42.99   $43.00   $43.00  
  Purchase #5 $105.65   6.707%   $112.7359   $112.74   $112.75   $112.70  
  Purchase #6 $112.79   5.586%   $119.0904   $119.09   $119.10   $119.10  
  Purchase #7 $237.47   13.230%   $268.8873   $268.89   $268.90   $268.90  
  7 purchase totals = $922.22       $1,003.2370   $1,003.24   $1,003.30   $1,003.20