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 $70.75   8.185%   $76.5409   $76.54   $76.55   $76.50  
  Purchase #2 $217.33   5.541%   $229.3723   $229.37   $229.35   $229.40  
  Purchase #3 $26.31   6.661%   $28.0625   $28.06   $28.05   $28.10  
  Purchase #4 $72.43   12.420%   $81.4258   $81.43   $81.45   $81.40  
  Purchase #5 $61.79   11.860%   $69.1183   $69.12   $69.10   $69.10  
  Purchase #6 $176.65   11.694%   $197.3075   $197.31   $197.30   $197.30  
  Purchase #7 $170.61   13.374%   $193.4274   $193.43   $193.45   $193.40  
  7 purchase totals = $795.87       $875.2547   $875.26   $875.25   $875.20