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 $87.74   8.121%   $94.8654   $94.87   $94.85   $94.90  
  Purchase #2 $195.26   10.289%   $215.3503   $215.35   $215.35   $215.40  
  Purchase #3 $191.46   11.833%   $214.1155   $214.12   $214.10   $214.10  
  Purchase #4 $95.73   13.387%   $108.5454   $108.55   $108.55   $108.50  
  Purchase #5 $24.33   9.515%   $26.645   $26.65   $26.65   $26.60  
  Purchase #6 $150.77   11.842%   $168.6242   $168.62   $168.60   $168.60  
  Purchase #7 $207.28   9.338%   $226.6358   $226.64   $226.65   $226.60  
  7 purchase totals = $952.57       $1,054.7816   $1,054.80   $1,054.75   $1,054.70