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 $58.36   11.723%   $65.2015   $65.20   $65.20   $65.20  
  Purchase #2 $72.65   11.308%   $80.8653   $80.87   $80.85   $80.90  
  Purchase #3 $116.77   7.805%   $125.8839   $125.88   $125.90   $125.90  
  Purchase #4 $229.88   3.321%   $237.5143   $237.51   $237.50   $237.50  
  Purchase #5 $128.91   8.334%   $139.6534   $139.65   $139.65   $139.70  
  Purchase #6 $67.29   9.572%   $73.731   $73.73   $73.75   $73.70  
  Purchase #7 $203.40   7.680%   $219.0211   $219.02   $219.00   $219.00  
  7 purchase totals = $877.26       $941.8705   $941.86   $941.85   $941.90