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 $77.47   5.466%   $81.7045   $81.70   $81.70   $81.70  
  Purchase #2 $64.69   12.850%   $73.0027   $73.00   $73.00   $73.00  
  Purchase #3 $185.95   11.136%   $206.6574   $206.66   $206.65   $206.70  
  Purchase #4 $243.82   4.677%   $255.2235   $255.22   $255.20   $255.20  
  Purchase #5 $199.60   7.607%   $214.7836   $214.78   $214.80   $214.80  
  Purchase #6 $225.88   12.544%   $254.2144   $254.21   $254.20   $254.20  
  Purchase #7 $111.54   4.256%   $116.2871   $116.29   $116.30   $116.30  
  7 purchase totals = $1,108.95       $1,201.8732   $1,201.86   $1,201.85   $1,201.90