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 $75.38   12.545%   $84.8364   $84.84   $84.85   $84.80  
  Purchase #2 $228.67   8.215%   $247.4552   $247.46   $247.45   $247.50  
  Purchase #3 $227.62   5.145%   $239.331   $239.33   $239.35   $239.30  
  Purchase #4 $87.34   9.428%   $95.5744   $95.57   $95.55   $95.60  
  Purchase #5 $153.44   4.186%   $159.863   $159.86   $159.85   $159.90  
  Purchase #6 $140.89   4.147%   $146.7327   $146.73   $146.75   $146.70  
  Purchase #7 $208.81   5.155%   $219.5742   $219.57   $219.55   $219.60  
  7 purchase totals = $1,122.15       $1,193.3669   $1,193.36   $1,193.35   $1,193.40