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 $86.63   8.698%   $94.1651   $94.17   $94.15   $94.20  
  Purchase #2 $248.50   13.743%   $282.6514   $282.65   $282.65   $282.70  
  Purchase #3 $28.64   11.761%   $32.0084   $32.01   $32.00   $32.00  
  Purchase #4 $178.80   9.385%   $195.5804   $195.58   $195.60   $195.60  
  Purchase #5 $166.42   9.338%   $181.9603   $181.96   $181.95   $182.00  
  Purchase #6 $151.56   6.772%   $161.8236   $161.82   $161.80   $161.80  
  Purchase #7 $246.87   9.320%   $269.8783   $269.88   $269.90   $269.90  
  7 purchase totals = $1,107.42       $1,218.0675   $1,218.07   $1,218.05   $1,218.20