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 $30.86   10.569%   $34.1216   $34.12   $34.10   $34.10  
  Purchase #2 $32.99   9.562%   $36.1445   $36.14   $36.15   $36.10  
  Purchase #3 $54.90   13.402%   $62.2577   $62.26   $62.25   $62.30  
  Purchase #4 $9.35   6.672%   $9.9738   $9.97   $9.95   $10.00  
  Purchase #5 $148.71   8.596%   $161.4931   $161.49   $161.50   $161.50  
  Purchase #6 $109.44   7.567%   $117.7213   $117.72   $117.70   $117.70  
  Purchase #7 $53.73   7.508%   $57.764   $57.76   $57.75   $57.80  
  7 purchase totals = $439.98       $479.4760   $479.46   $479.40   $479.50