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 $232.26   6.627%   $247.6519   $247.65   $247.65   $247.70  
  Purchase #2 $155.27   7.394%   $166.7507   $166.75   $166.75   $166.80  
  Purchase #3 $192.73   6.838%   $205.9089   $205.91   $205.90   $205.90  
  Purchase #4 $239.51   10.783%   $265.3364   $265.34   $265.35   $265.30  
  Purchase #5 $170.81   10.858%   $189.3565   $189.36   $189.35   $189.40  
  Purchase #6 $124.63   5.123%   $131.0148   $131.01   $131.00   $131.00  
  Purchase #7 $74.86   3.242%   $77.287   $77.29   $77.30   $77.30  
  7 purchase totals = $1,190.07       $1,283.3062   $1,283.31   $1,283.30   $1,283.40