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 $202.25   12.605%   $227.7436   $227.74   $227.75   $227.70  
  Purchase #2 $14.57   9.786%   $15.9958   $16.00   $16.00   $16.00  
  Purchase #3 $194.70   6.321%   $207.007   $207.01   $207.00   $207.00  
  Purchase #4 $62.95   9.507%   $68.9347   $68.93   $68.95   $68.90  
  Purchase #5 $121.90   8.825%   $132.6577   $132.66   $132.65   $132.70  
  Purchase #6 $65.88   4.467%   $68.8229   $68.82   $68.80   $68.80  
  Purchase #7 $103.66   4.553%   $108.3796   $108.38   $108.40   $108.40  
  7 purchase totals = $765.91       $829.5413   $829.54   $829.55   $829.50