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 $208.72   10.643%   $230.9341   $230.93   $230.95   $230.90  
  Purchase #2 $197.57   13.141%   $223.5327   $223.53   $223.55   $223.50  
  Purchase #3 $104.28   12.201%   $117.0032   $117.00   $117.00   $117.00  
  Purchase #4 $13.43   9.238%   $14.6707   $14.67   $14.65   $14.70  
  Purchase #5 $29.68   6.614%   $31.643   $31.64   $31.65   $31.60  
  Purchase #6 $195.42   5.680%   $206.5199   $206.52   $206.50   $206.50  
  Purchase #7 $17.31   3.366%   $17.8927   $17.89   $17.90   $17.90  
  7 purchase totals = $766.41       $842.1963   $842.18   $842.20   $842.10