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 $135.63   3.747%   $140.7121   $140.71   $140.70   $140.70  
  Purchase #2 $243.61   3.748%   $252.7405   $252.74   $252.75   $252.70  
  Purchase #3 $98.76   11.410%   $110.0285   $110.03   $110.05   $110.00  
  Purchase #4 $203.65   9.305%   $222.5996   $222.60   $222.60   $222.60  
  Purchase #5 $189.51   3.817%   $196.7436   $196.74   $196.75   $196.70  
  Purchase #6 $99.71   12.813%   $112.4858   $112.49   $112.50   $112.50  
  Purchase #7 $184.48   13.425%   $209.2464   $209.25   $209.25   $209.20  
  7 purchase totals = $1,155.35       $1,244.5565   $1,244.56   $1,244.60   $1,244.40