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 $245.61   9.411%   $268.7244   $268.72   $268.70   $268.70  
  Purchase #2 $24.49   9.312%   $26.7705   $26.77   $26.75   $26.80  
  Purchase #3 $204.38   10.546%   $225.9339   $225.93   $225.95   $225.90  
  Purchase #4 $162.69   8.171%   $175.9834   $175.98   $176.00   $176.00  
  Purchase #5 $225.49   3.782%   $234.018   $234.02   $234.00   $234.00  
  Purchase #6 $87.33   9.446%   $95.5792   $95.58   $95.60   $95.60  
  Purchase #7 $19.72   3.533%   $20.4167   $20.42   $20.40   $20.40  
  7 purchase totals = $969.71       $1,047.4261   $1,047.42   $1,047.40   $1,047.40