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 $119.52   9.808%   $131.2425   $131.24   $131.25   $131.20  
  Purchase #2 $108.69   13.205%   $123.0425   $123.04   $123.05   $123.00  
  Purchase #3 $223.47   5.738%   $236.2927   $236.29   $236.30   $236.30  
  Purchase #4 $191.29   8.507%   $207.563   $207.56   $207.55   $207.60  
  Purchase #5 $171.80   7.535%   $184.7451   $184.75   $184.75   $184.70  
  Purchase #6 $250.60   5.719%   $264.9318   $264.93   $264.95   $264.90  
  Purchase #7 $97.71   11.530%   $108.976   $108.98   $109.00   $109.00  
  7 purchase totals = $1,163.08       $1,256.7936   $1,256.79   $1,256.85   $1,256.70