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 $58.39   13.486%   $66.2645   $66.26   $66.25   $66.30  
  Purchase #2 $171.41   11.721%   $191.501   $191.50   $191.50   $191.50  
  Purchase #3 $172.37   8.690%   $187.349   $187.35   $187.35   $187.30  
  Purchase #4 $77.47   5.814%   $81.9741   $81.97   $81.95   $82.00  
  Purchase #5 $142.33   9.322%   $155.598   $155.60   $155.60   $155.60  
  Purchase #6 $167.42   6.528%   $178.3492   $178.35   $178.35   $178.30  
  Purchase #7 $145.76   10.701%   $161.3578   $161.36   $161.35   $161.40  
  7 purchase totals = $935.15       $1,022.3936   $1,022.39   $1,022.35   $1,022.40