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 $66.48   10.307%   $73.3321   $73.33   $73.35   $73.30  
  Purchase #2 $176.36   12.641%   $198.6537   $198.65   $198.65   $198.70  
  Purchase #3 $219.44   6.103%   $232.8324   $232.83   $232.85   $232.80  
  Purchase #4 $228.64   3.347%   $236.2926   $236.29   $236.30   $236.30  
  Purchase #5 $137.97   7.506%   $148.326   $148.33   $148.35   $148.30  
  Purchase #6 $247.37   5.221%   $260.2852   $260.29   $260.30   $260.30  
  Purchase #7 $214.63   12.400%   $241.2441   $241.24   $241.25   $241.20  
  7 purchase totals = $1,290.89       $1,390.9661   $1,390.96   $1,391.05   $1,390.90