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 $183.94   11.679%   $205.4224   $205.42   $205.40   $205.40  
  Purchase #2 $175.89   8.707%   $191.2047   $191.20   $191.20   $191.20  
  Purchase #3 $241.86   3.253%   $249.7277   $249.73   $249.75   $249.70  
  Purchase #4 $119.47   4.347%   $124.6634   $124.66   $124.65   $124.70  
  Purchase #5 $106.36   10.869%   $117.9203   $117.92   $117.90   $117.90  
  Purchase #6 $71.93   4.701%   $75.3114   $75.31   $75.30   $75.30  
  Purchase #7 $119.27   11.525%   $133.0159   $133.02   $133.00   $133.00  
  7 purchase totals = $1,018.72       $1,097.2658   $1,097.26   $1,097.20   $1,097.20