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 $60.29   8.869%   $65.6371   $65.64   $65.65   $65.60  
  Purchase #2 $72.38   3.585%   $74.9748   $74.97   $74.95   $75.00  
  Purchase #3 $90.58   5.125%   $95.2222   $95.22   $95.20   $95.20  
  Purchase #4 $235.93   7.874%   $254.5071   $254.51   $254.50   $254.50  
  Purchase #5 $136.72   11.507%   $152.4524   $152.45   $152.45   $152.50  
  Purchase #6 $172.59   10.842%   $191.3022   $191.30   $191.30   $191.30  
  Purchase #7 $97.79   13.504%   $110.9956   $111.00   $111.00   $111.00  
  7 purchase totals = $866.28       $945.0914   $945.09   $945.05   $945.10