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 $194.35   12.665%   $218.9644   $218.96   $218.95   $219.00  
  Purchase #2 $120.62   8.242%   $130.5615   $130.56   $130.55   $130.60  
  Purchase #3 $123.30   12.723%   $138.9875   $138.99   $139.00   $139.00  
  Purchase #4 $70.47   8.455%   $76.4282   $76.43   $76.45   $76.40  
  Purchase #5 $249.97   8.783%   $271.9249   $271.92   $271.90   $271.90  
  Purchase #6 $187.63   12.701%   $211.4609   $211.46   $211.45   $211.50  
  Purchase #7 $88.36   8.627%   $95.9828   $95.98   $96.00   $96.00  
  7 purchase totals = $1,034.70       $1,144.3102   $1,144.30   $1,144.30   $1,144.40