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 $67.63   8.760%   $73.5544   $73.55   $73.55   $73.60  
  Purchase #2 $58.85   13.767%   $66.9519   $66.95   $66.95   $67.00  
  Purchase #3 $124.42   3.658%   $128.9713   $128.97   $128.95   $129.00  
  Purchase #4 $168.29   12.705%   $189.6712   $189.67   $189.65   $189.70  
  Purchase #5 $118.42   11.483%   $132.0182   $132.02   $132.00   $132.00  
  Purchase #6 $205.45   8.277%   $222.4551   $222.46   $222.45   $222.50  
  Purchase #7 $240.98   7.581%   $259.2487   $259.25   $259.25   $259.20  
  7 purchase totals = $984.04       $1,072.8708   $1,072.87   $1,072.80   $1,073.00