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 $211.73   6.261%   $224.9864   $224.99   $225.00   $225.00  
  Purchase #2 $240.64   12.742%   $271.3023   $271.30   $271.30   $271.30  
  Purchase #3 $211.73   7.809%   $228.264   $228.26   $228.25   $228.30  
  Purchase #4 $122.88   9.216%   $134.2046   $134.20   $134.20   $134.20  
  Purchase #5 $250.40   7.742%   $269.786   $269.79   $269.80   $269.80  
  Purchase #6 $72.51   3.426%   $74.9942   $74.99   $75.00   $75.00  
  Purchase #7 $122.86   8.521%   $133.3289   $133.33   $133.35   $133.30  
  7 purchase totals = $1,232.75       $1,336.8664   $1,336.86   $1,336.90   $1,336.90