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 $200.29   6.448%   $213.2047   $213.20   $213.20   $213.20  
  Purchase #2 $169.26   4.549%   $176.9596   $176.96   $176.95   $177.00  
  Purchase #3 $24.50   7.702%   $26.387   $26.39   $26.40   $26.40  
  Purchase #4 $195.67   10.717%   $216.64   $216.64   $216.65   $216.60  
  Purchase #5 $105.44   13.349%   $119.5152   $119.52   $119.50   $119.50  
  Purchase #6 $158.94   9.698%   $174.354   $174.35   $174.35   $174.40  
  Purchase #7 $43.75   10.779%   $48.4658   $48.47   $48.45   $48.50  
  7 purchase totals = $897.85       $975.5263   $975.53   $975.50   $975.60