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 $60.92   8.207%   $65.9197   $65.92   $65.90   $65.90  
  Purchase #2 $102.51   8.571%   $111.2961   $111.30   $111.30   $111.30  
  Purchase #3 $167.48   8.143%   $181.1179   $181.12   $181.10   $181.10  
  Purchase #4 $93.38   3.600%   $96.7417   $96.74   $96.75   $96.70  
  Purchase #5 $223.42   12.135%   $250.532   $250.53   $250.55   $250.50  
  Purchase #6 $32.39   10.468%   $35.7806   $35.78   $35.80   $35.80  
  Purchase #7 $95.82   5.609%   $101.1945   $101.19   $101.20   $101.20  
  7 purchase totals = $775.92       $842.5825   $842.58   $842.60   $842.50