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 $190.69   11.729%   $213.056   $213.06   $213.05   $213.10  
  Purchase #2 $32.45   10.372%   $35.8157   $35.82   $35.80   $35.80  
  Purchase #3 $176.38   8.835%   $191.9632   $191.96   $191.95   $192.00  
  Purchase #4 $113.81   3.800%   $118.1348   $118.13   $118.15   $118.10  
  Purchase #5 $231.32   10.530%   $255.678   $255.68   $255.70   $255.70  
  Purchase #6 $221.54   12.492%   $249.2148   $249.21   $249.20   $249.20  
  Purchase #7 $59.39   9.525%   $65.0469   $65.05   $65.05   $65.00  
  7 purchase totals = $1,025.58       $1,128.9094   $1,128.91   $1,128.90   $1,128.90