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 $32.40   13.244%   $36.6911   $36.69   $36.70   $36.70  
  Purchase #2 $201.85   11.134%   $224.324   $224.32   $224.30   $224.30  
  Purchase #3 $64.71   3.141%   $66.7425   $66.74   $66.75   $66.70  
  Purchase #4 $184.40   7.631%   $198.4716   $198.47   $198.45   $198.50  
  Purchase #5 $113.65   11.303%   $126.4959   $126.50   $126.50   $126.50  
  Purchase #6 $191.88   11.570%   $214.0805   $214.08   $214.10   $214.10  
  Purchase #7 $230.81   11.277%   $256.8384   $256.84   $256.85   $256.80  
  7 purchase totals = $1,019.70       $1,123.6440   $1,123.64   $1,123.65   $1,123.60