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 $47.33   6.743%   $50.5215   $50.52   $50.50   $50.50  
  Purchase #2 $156.30   11.635%   $174.4855   $174.49   $174.50   $174.50  
  Purchase #3 $34.31   8.731%   $37.3056   $37.31   $37.30   $37.30  
  Purchase #4 $242.26   10.693%   $268.1649   $268.16   $268.15   $268.20  
  Purchase #5 $117.73   6.553%   $125.4448   $125.44   $125.45   $125.40  
  Purchase #6 $218.38   12.355%   $245.3608   $245.36   $245.35   $245.40  
  Purchase #7 $116.47   3.463%   $120.5034   $120.50   $120.50   $120.50  
  7 purchase totals = $932.78       $1,021.7865   $1,021.78   $1,021.75   $1,021.80