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 $67.80   11.672%   $75.7136   $75.71   $75.70   $75.70  
  Purchase #2 $212.95   13.779%   $242.2924   $242.29   $242.30   $242.30  
  Purchase #3 $69.33   6.725%   $73.9924   $73.99   $74.00   $74.00  
  Purchase #4 $121.72   8.694%   $132.3023   $132.30   $132.30   $132.30  
  Purchase #5 $68.79   7.661%   $74.06   $74.06   $74.05   $74.10  
  Purchase #6 $171.39   3.144%   $176.7785   $176.78   $176.80   $176.80  
  Purchase #7 $10.49   12.599%   $11.8116   $11.81   $11.80   $11.80  
  7 purchase totals = $722.47       $786.9508   $786.94   $786.95   $787.00