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 $130.42   8.262%   $141.1953   $141.20   $141.20   $141.20  
  Purchase #2 $72.63   9.193%   $79.3069   $79.31   $79.30   $79.30  
  Purchase #3 $9.73   6.621%   $10.3742   $10.37   $10.35   $10.40  
  Purchase #4 $198.54   5.408%   $209.277   $209.28   $209.30   $209.30  
  Purchase #5 $84.42   13.204%   $95.5668   $95.57   $95.55   $95.60  
  Purchase #6 $80.87   13.555%   $91.8319   $91.83   $91.85   $91.80  
  Purchase #7 $244.33   10.330%   $269.5693   $269.57   $269.55   $269.60  
  7 purchase totals = $820.94       $897.1214   $897.13   $897.10   $897.20