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 $204.33   9.471%   $223.6821   $223.68   $223.70   $223.70  
  Purchase #2 $141.26   12.122%   $158.3835   $158.38   $158.40   $158.40  
  Purchase #3 $165.90   7.214%   $177.868   $177.87   $177.85   $177.90  
  Purchase #4 $246.25   11.331%   $274.1526   $274.15   $274.15   $274.20  
  Purchase #5 $16.34   13.385%   $18.5271   $18.53   $18.55   $18.50  
  Purchase #6 $104.46   11.368%   $116.335   $116.34   $116.35   $116.30  
  Purchase #7 $112.79   4.483%   $117.8464   $117.85   $117.85   $117.80  
  7 purchase totals = $991.33       $1,086.7947   $1,086.80   $1,086.85   $1,086.80