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 $56.90   6.482%   $60.5883   $60.59   $60.60   $60.60  
  Purchase #2 $166.87   10.252%   $183.9775   $183.98   $184.00   $184.00  
  Purchase #3 $136.92   7.192%   $146.7673   $146.77   $146.75   $146.80  
  Purchase #4 $222.88   8.183%   $241.1183   $241.12   $241.10   $241.10  
  Purchase #5 $96.42   9.538%   $105.6165   $105.62   $105.60   $105.60  
  Purchase #6 $90.94   8.268%   $98.4589   $98.46   $98.45   $98.50  
  Purchase #7 $225.50   8.721%   $245.1659   $245.17   $245.15   $245.20  
  7 purchase totals = $996.43       $1,081.6927   $1,081.71   $1,081.65   $1,081.80