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 $83.45   13.593%   $94.7934   $94.79   $94.80   $94.80  
  Purchase #2 $174.44   13.808%   $198.5267   $198.53   $198.55   $198.50  
  Purchase #3 $26.90   9.612%   $29.4856   $29.49   $29.50   $29.50  
  Purchase #4 $202.85   8.196%   $219.4756   $219.48   $219.50   $219.50  
  Purchase #5 $196.47   6.328%   $208.9026   $208.90   $208.90   $208.90  
  Purchase #6 $142.50   13.645%   $161.9441   $161.94   $161.95   $161.90  
  Purchase #7 $139.33   7.353%   $149.5749   $149.57   $149.55   $149.60  
  7 purchase totals = $965.94       $1,062.7029   $1,062.70   $1,062.75   $1,062.70