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 $227.80   11.771%   $254.6143   $254.61   $254.60   $254.60  
  Purchase #2 $24.41   4.666%   $25.549   $25.55   $25.55   $25.50  
  Purchase #3 $116.97   3.430%   $120.9821   $120.98   $121.00   $121.00  
  Purchase #4 $208.78   4.287%   $217.7304   $217.73   $217.75   $217.70  
  Purchase #5 $142.49   5.667%   $150.5649   $150.56   $150.55   $150.60  
  Purchase #6 $60.89   7.151%   $65.2442   $65.24   $65.25   $65.20  
  Purchase #7 $201.89   6.269%   $214.5465   $214.55   $214.55   $214.50  
  7 purchase totals = $983.23       $1,049.2314   $1,049.22   $1,049.25   $1,049.10