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 $241.38   10.693%   $267.1908   $267.19   $267.20   $267.20  
  Purchase #2 $243.40   9.468%   $266.4451   $266.45   $266.45   $266.40  
  Purchase #3 $138.68   7.617%   $149.2433   $149.24   $149.25   $149.20  
  Purchase #4 $132.84   9.350%   $145.2605   $145.26   $145.25   $145.30  
  Purchase #5 $68.31   12.622%   $76.9321   $76.93   $76.95   $76.90  
  Purchase #6 $27.34   13.398%   $31.003   $31.00   $31.00   $31.00  
  Purchase #7 $187.89   13.432%   $213.1274   $213.13   $213.15   $213.10  
  7 purchase totals = $1,039.84       $1,149.2022   $1,149.20   $1,149.25   $1,149.10