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 $244.55   8.219%   $264.6496   $264.65   $264.65   $264.60  
  Purchase #2 $73.96   3.152%   $76.2912   $76.29   $76.30   $76.30  
  Purchase #3 $136.25   4.225%   $142.0066   $142.01   $142.00   $142.00  
  Purchase #4 $145.76   4.561%   $152.4081   $152.41   $152.40   $152.40  
  Purchase #5 $29.52   11.665%   $32.9635   $32.96   $32.95   $33.00  
  Purchase #6 $116.93   11.357%   $130.2097   $130.21   $130.20   $130.20  
  Purchase #7 $130.47   4.849%   $136.7965   $136.80   $136.80   $136.80  
  7 purchase totals = $877.44       $935.3252   $935.33   $935.30   $935.30