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 $22.53   10.844%   $24.9732   $24.97   $24.95   $25.00  
  Purchase #2 $154.84   3.156%   $159.7268   $159.73   $159.75   $159.70  
  Purchase #3 $167.84   11.138%   $186.534   $186.53   $186.55   $186.50  
  Purchase #4 $141.72   13.161%   $160.3718   $160.37   $160.35   $160.40  
  Purchase #5 $65.67   7.277%   $70.4488   $70.45   $70.45   $70.40  
  Purchase #6 $160.62   7.604%   $172.8335   $172.83   $172.85   $172.80  
  Purchase #7 $87.59   13.151%   $99.109   $99.11   $99.10   $99.10  
  7 purchase totals = $800.81       $873.9971   $873.99   $874.00   $873.90