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 $146.80   10.764%   $162.6016   $162.60   $162.60   $162.60  
  Purchase #2 $204.41   3.409%   $211.3783   $211.38   $211.40   $211.40  
  Purchase #3 $7.78   4.430%   $8.1247   $8.12   $8.10   $8.10  
  Purchase #4 $220.37   5.360%   $232.1818   $232.18   $232.20   $232.20  
  Purchase #5 $179.70   13.169%   $203.3647   $203.36   $203.35   $203.40  
  Purchase #6 $227.69   10.322%   $251.1922   $251.19   $251.20   $251.20  
  Purchase #7 $42.55   10.262%   $46.9165   $46.92   $46.90   $46.90  
  7 purchase totals = $1,029.30       $1,115.7598   $1,115.75   $1,115.75   $1,115.80