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 $248.78   13.684%   $282.8231   $282.82   $282.80   $282.80  
  Purchase #2 $225.93   8.854%   $245.9338   $245.93   $245.95   $245.90  
  Purchase #3 $233.71   8.818%   $254.3185   $254.32   $254.30   $254.30  
  Purchase #4 $87.96   5.677%   $92.9535   $92.95   $92.95   $93.00  
  Purchase #5 $105.99   8.585%   $115.0892   $115.09   $115.10   $115.10  
  Purchase #6 $26.64   6.120%   $28.2704   $28.27   $28.25   $28.30  
  Purchase #7 $34.35   7.536%   $36.9386   $36.94   $36.95   $36.90  
  7 purchase totals = $963.36       $1,056.3271   $1,056.32   $1,056.30   $1,056.30