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 $188.96   8.273%   $204.5927   $204.59   $204.60   $204.60  
  Purchase #2 $117.73   6.573%   $125.4684   $125.47   $125.45   $125.50  
  Purchase #3 $209.91   7.487%   $225.626   $225.63   $225.65   $225.60  
  Purchase #4 $66.31   9.592%   $72.6705   $72.67   $72.65   $72.70  
  Purchase #5 $200.71   11.617%   $224.0265   $224.03   $224.05   $224.00  
  Purchase #6 $60.74   10.389%   $67.0503   $67.05   $67.05   $67.10  
  Purchase #7 $206.84   5.240%   $217.6784   $217.68   $217.70   $217.70  
  7 purchase totals = $1,051.20       $1,137.1128   $1,137.12   $1,137.15   $1,137.20