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 $107.87   10.769%   $119.4865   $119.49   $119.50   $119.50  
  Purchase #2 $247.77   9.346%   $270.9266   $270.93   $270.95   $270.90  
  Purchase #3 $16.29   13.776%   $18.5341   $18.53   $18.55   $18.50  
  Purchase #4 $85.46   6.235%   $90.7884   $90.79   $90.80   $90.80  
  Purchase #5 $113.67   9.508%   $124.4777   $124.48   $124.50   $124.50  
  Purchase #6 $232.74   10.408%   $256.9636   $256.96   $256.95   $257.00  
  Purchase #7 $178.49   5.238%   $187.8393   $187.84   $187.85   $187.80  
  7 purchase totals = $982.29       $1,069.0162   $1,069.02   $1,069.10   $1,069.00