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 $233.69   12.783%   $263.5626   $263.56   $263.55   $263.60  
  Purchase #2 $43.65   13.872%   $49.7051   $49.71   $49.70   $49.70  
  Purchase #3 $94.40   5.759%   $99.8365   $99.84   $99.85   $99.80  
  Purchase #4 $13.71   12.247%   $15.3891   $15.39   $15.40   $15.40  
  Purchase #5 $161.75   6.218%   $171.8076   $171.81   $171.80   $171.80  
  Purchase #6 $220.40   4.357%   $230.0028   $230.00   $230.00   $230.00  
  Purchase #7 $112.27   10.347%   $123.8866   $123.89   $123.90   $123.90  
  7 purchase totals = $879.87       $954.1903   $954.20   $954.20   $954.20