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 $170.83   13.781%   $194.3721   $194.37   $194.35   $194.40  
  Purchase #2 $232.98   13.838%   $265.2198   $265.22   $265.20   $265.20  
  Purchase #3 $153.74   5.832%   $162.7061   $162.71   $162.70   $162.70  
  Purchase #4 $209.55   11.837%   $234.3544   $234.35   $234.35   $234.40  
  Purchase #5 $193.62   6.530%   $206.2634   $206.26   $206.25   $206.30  
  Purchase #6 $141.63   13.524%   $160.784   $160.78   $160.80   $160.80  
  Purchase #7 $167.56   6.345%   $178.1917   $178.19   $178.20   $178.20  
  7 purchase totals = $1,269.91       $1,401.8915   $1,401.88   $1,401.85   $1,402.00