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 $208.35   11.666%   $232.6561   $232.66   $232.65   $232.70  
  Purchase #2 $32.84   3.497%   $33.9884   $33.99   $34.00   $34.00  
  Purchase #3 $141.62   13.838%   $161.2174   $161.22   $161.20   $161.20  
  Purchase #4 $114.84   5.496%   $121.1516   $121.15   $121.15   $121.20  
  Purchase #5 $94.50   6.162%   $100.3231   $100.32   $100.30   $100.30  
  Purchase #6 $219.39   11.614%   $244.87   $244.87   $244.85   $244.90  
  Purchase #7 $126.91   5.614%   $134.0347   $134.03   $134.05   $134.00  
  7 purchase totals = $938.45       $1,028.2413   $1,028.24   $1,028.20   $1,028.30