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 $24.40   10.620%   $26.9913   $26.99   $27.00   $27.00  
  Purchase #2 $244.66   6.262%   $259.9806   $259.98   $260.00   $260.00  
  Purchase #3 $223.97   7.435%   $240.6222   $240.62   $240.60   $240.60  
  Purchase #4 $86.39   10.426%   $95.397   $95.40   $95.40   $95.40  
  Purchase #5 $157.75   8.800%   $171.632   $171.63   $171.65   $171.60  
  Purchase #6 $183.48   5.331%   $193.2613   $193.26   $193.25   $193.30  
  Purchase #7 $89.35   11.658%   $99.7664   $99.77   $99.75   $99.80  
  7 purchase totals = $1,010.00       $1,087.6508   $1,087.65   $1,087.65   $1,087.70