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 $211.92   6.292%   $225.254   $225.25   $225.25   $225.30  
  Purchase #2 $16.67   10.754%   $18.4627   $18.46   $18.45   $18.50  
  Purchase #3 $218.72   6.236%   $232.3594   $232.36   $232.35   $232.40  
  Purchase #4 $198.71   4.328%   $207.3102   $207.31   $207.30   $207.30  
  Purchase #5 $217.81   13.376%   $246.9443   $246.94   $246.95   $246.90  
  Purchase #6 $134.55   11.318%   $149.7784   $149.78   $149.80   $149.80  
  Purchase #7 $151.66   3.185%   $156.4904   $156.49   $156.50   $156.50  
  7 purchase totals = $1,150.04       $1,236.5994   $1,236.59   $1,236.60   $1,236.70