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 $208.92   13.230%   $236.5601   $236.56   $236.55   $236.60  
  Purchase #2 $154.34   9.214%   $168.5609   $168.56   $168.55   $168.60  
  Purchase #3 $67.61   4.467%   $70.6301   $70.63   $70.65   $70.60  
  Purchase #4 $84.78   13.618%   $96.3253   $96.33   $96.35   $96.30  
  Purchase #5 $149.90   6.360%   $159.4336   $159.43   $159.45   $159.40  
  Purchase #6 $198.80   11.243%   $221.1511   $221.15   $221.15   $221.20  
  Purchase #7 $72.91   3.813%   $75.6901   $75.69   $75.70   $75.70  
  7 purchase totals = $937.26       $1,028.3512   $1,028.35   $1,028.40   $1,028.40