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 $203.47   5.445%   $214.5489   $214.55   $214.55   $214.50  
  Purchase #2 $25.89   5.428%   $27.2953   $27.30   $27.30   $27.30  
  Purchase #3 $73.61   11.333%   $81.9522   $81.95   $81.95   $82.00  
  Purchase #4 $94.95   4.822%   $99.5285   $99.53   $99.55   $99.50  
  Purchase #5 $163.37   12.140%   $183.2031   $183.20   $183.20   $183.20  
  Purchase #6 $246.74   12.659%   $277.9748   $277.97   $277.95   $278.00  
  Purchase #7 $34.47   6.753%   $36.7978   $36.80   $36.80   $36.80  
  7 purchase totals = $842.50       $921.3006   $921.30   $921.30   $921.30