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 $248.62   13.741%   $282.7829   $282.78   $282.80   $282.80  
  Purchase #2 $188.47   12.118%   $211.3088   $211.31   $211.30   $211.30  
  Purchase #3 $96.46   8.526%   $104.6842   $104.68   $104.70   $104.70  
  Purchase #4 $46.67   13.825%   $53.1221   $53.12   $53.10   $53.10  
  Purchase #5 $104.26   12.408%   $117.1966   $117.20   $117.20   $117.20  
  Purchase #6 $119.26   3.148%   $123.0143   $123.01   $123.00   $123.00  
  Purchase #7 $100.80   6.501%   $107.353   $107.35   $107.35   $107.40  
  7 purchase totals = $904.54       $999.4619   $999.45   $999.45   $999.50