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 $112.93   12.322%   $126.8452   $126.85   $126.85   $126.80  
  Purchase #2 $186.71   5.314%   $196.6318   $196.63   $196.65   $196.60  
  Purchase #3 $115.64   9.270%   $126.3598   $126.36   $126.35   $126.40  
  Purchase #4 $55.78   12.356%   $62.6722   $62.67   $62.65   $62.70  
  Purchase #5 $165.59   13.199%   $187.4462   $187.45   $187.45   $187.40  
  Purchase #6 $220.55   7.852%   $237.8676   $237.87   $237.85   $237.90  
  Purchase #7 $21.51   9.361%   $23.5236   $23.52   $23.50   $23.50  
  7 purchase totals = $878.71       $961.3464   $961.35   $961.30   $961.30