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 $37.97   8.210%   $41.0873   $41.09   $41.10   $41.10  
  Purchase #2 $171.88   7.151%   $184.1711   $184.17   $184.15   $184.20  
  Purchase #3 $250.29   3.313%   $258.5821   $258.58   $258.60   $258.60  
  Purchase #4 $194.80   3.188%   $201.0102   $201.01   $201.00   $201.00  
  Purchase #5 $96.47   5.473%   $101.7498   $101.75   $101.75   $101.70  
  Purchase #6 $208.42   8.141%   $225.3875   $225.39   $225.40   $225.40  
  Purchase #7 $58.83   10.709%   $65.1301   $65.13   $65.15   $65.10  
  7 purchase totals = $1,018.66       $1,077.1181   $1,077.12   $1,077.15   $1,077.10