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   6.437%   $202.9647   $202.96   $202.95   $203.00  
  Purchase #2 $112.47   10.337%   $124.096   $124.10   $124.10   $124.10  
  Purchase #3 $61.94   6.355%   $65.8763   $65.88   $65.90   $65.90  
  Purchase #4 $168.67   3.804%   $175.0862   $175.09   $175.10   $175.10  
  Purchase #5 $117.87   13.719%   $134.0406   $134.04   $134.05   $134.00  
  Purchase #6 $86.34   5.388%   $90.992   $90.99   $91.00   $91.00  
  Purchase #7 $198.39   6.569%   $211.4222   $211.42   $211.40   $211.40  
  7 purchase totals = $936.37       $1,004.4780   $1,004.48   $1,004.50   $1,004.50