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 $88.78   8.366%   $96.2073   $96.21   $96.20   $96.20  
  Purchase #2 $236.64   12.184%   $265.4722   $265.47   $265.45   $265.50  
  Purchase #3 $213.97   7.562%   $230.1504   $230.15   $230.15   $230.20  
  Purchase #4 $85.49   7.798%   $92.1565   $92.16   $92.15   $92.20  
  Purchase #5 $153.54   5.751%   $162.3701   $162.37   $162.35   $162.40  
  Purchase #6 $135.80   4.106%   $141.3759   $141.38   $141.40   $141.40  
  Purchase #7 $153.36   6.184%   $162.8438   $162.84   $162.85   $162.80  
  7 purchase totals = $1,067.58       $1,150.5762   $1,150.58   $1,150.55   $1,150.70