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 $86.68   8.266%   $93.845   $93.85   $93.85   $93.80  
  Purchase #2 $173.75   4.619%   $181.7755   $181.78   $181.80   $181.80  
  Purchase #3 $142.69   8.317%   $154.5575   $154.56   $154.55   $154.60  
  Purchase #4 $119.86   10.801%   $132.8061   $132.81   $132.80   $132.80  
  Purchase #5 $191.28   12.707%   $215.5859   $215.59   $215.60   $215.60  
  Purchase #6 $49.60   11.581%   $55.3442   $55.34   $55.35   $55.30  
  Purchase #7 $15.66   5.753%   $16.5609   $16.56   $16.55   $16.60  
  7 purchase totals = $779.52       $850.4751   $850.49   $850.50   $850.50