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 $194.35   8.722%   $211.3012   $211.30   $211.30   $211.30  
  Purchase #2 $137.97   3.607%   $142.9466   $142.95   $142.95   $142.90  
  Purchase #3 $93.78   6.622%   $99.9901   $99.99   $100.00   $100.00  
  Purchase #4 $197.38   9.705%   $216.5357   $216.54   $216.55   $216.50  
  Purchase #5 $57.98   5.131%   $60.955   $60.96   $60.95   $61.00  
  Purchase #6 $150.87   4.814%   $158.1329   $158.13   $158.15   $158.10  
  Purchase #7 $149.84   6.595%   $159.7219   $159.72   $159.70   $159.70  
  7 purchase totals = $982.17       $1,049.5834   $1,049.59   $1,049.60   $1,049.50