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 $95.71   6.204%   $101.6478   $101.65   $101.65   $101.60  
  Purchase #2 $231.96   8.442%   $251.5421   $251.54   $251.55   $251.50  
  Purchase #3 $230.85   3.277%   $238.415   $238.42   $238.40   $238.40  
  Purchase #4 $135.36   10.116%   $149.053   $149.05   $149.05   $149.10  
  Purchase #5 $197.31   9.853%   $216.751   $216.75   $216.75   $216.80  
  Purchase #6 $222.59   6.238%   $236.4752   $236.48   $236.50   $236.50  
  Purchase #7 $63.89   6.459%   $68.0167   $68.02   $68.00   $68.00  
  7 purchase totals = $1,177.67       $1,261.9008   $1,261.91   $1,261.90   $1,261.90