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 $229.97   13.811%   $261.7312   $261.73   $261.75   $261.70  
  Purchase #2 $58.85   11.764%   $65.7731   $65.77   $65.75   $65.80  
  Purchase #3 $162.31   3.128%   $167.3871   $167.39   $167.40   $167.40  
  Purchase #4 $149.99   4.253%   $156.3691   $156.37   $156.35   $156.40  
  Purchase #5 $161.72   8.112%   $174.8387   $174.84   $174.85   $174.80  
  Purchase #6 $112.47   4.738%   $117.7988   $117.80   $117.80   $117.80  
  Purchase #7 $54.84   3.335%   $56.6689   $56.67   $56.65   $56.70  
  7 purchase totals = $930.15       $1,000.5669   $1,000.57   $1,000.55   $1,000.60