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 $206.33   13.143%   $233.448   $233.45   $233.45   $233.40  
  Purchase #2 $184.71   10.539%   $204.1766   $204.18   $204.20   $204.20  
  Purchase #3 $120.94   8.564%   $131.2973   $131.30   $131.30   $131.30  
  Purchase #4 $159.63   13.863%   $181.7595   $181.76   $181.75   $181.80  
  Purchase #5 $25.33   10.219%   $27.9185   $27.92   $27.90   $27.90  
  Purchase #6 $127.39   6.760%   $136.0016   $136.00   $136.00   $136.00  
  Purchase #7 $59.32   3.149%   $61.188   $61.19   $61.20   $61.20  
  7 purchase totals = $883.65       $975.7895   $975.80   $975.80   $975.80