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 $101.53   6.818%   $108.4523   $108.45   $108.45   $108.50  
  Purchase #2 $226.77   8.367%   $245.7438   $245.74   $245.75   $245.70  
  Purchase #3 $183.27   11.632%   $204.588   $204.59   $204.60   $204.60  
  Purchase #4 $104.34   11.340%   $116.1722   $116.17   $116.15   $116.20  
  Purchase #5 $142.36   6.651%   $151.8284   $151.83   $151.85   $151.80  
  Purchase #6 $206.36   9.459%   $225.8796   $225.88   $225.90   $225.90  
  Purchase #7 $40.76   8.847%   $44.366   $44.37   $44.35   $44.40  
  7 purchase totals = $1,005.39       $1,097.0303   $1,097.03   $1,097.05   $1,097.10