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 $206.52   3.791%   $214.3492   $214.35   $214.35   $214.30  
  Purchase #2 $58.72   7.520%   $63.1357   $63.14   $63.15   $63.10  
  Purchase #3 $237.60   7.833%   $256.2112   $256.21   $256.20   $256.20  
  Purchase #4 $61.70   11.757%   $68.9541   $68.95   $68.95   $69.00  
  Purchase #5 $133.77   13.586%   $151.944   $151.94   $151.95   $151.90  
  Purchase #6 $246.48   11.310%   $274.3569   $274.36   $274.35   $274.40  
  Purchase #7 $196.69   5.423%   $207.3565   $207.36   $207.35   $207.40  
  7 purchase totals = $1,141.48       $1,236.3076   $1,236.31   $1,236.30   $1,236.30