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 $87.61   8.721%   $95.2505   $95.25   $95.25   $95.30  
  Purchase #2 $217.82   12.275%   $244.5574   $244.56   $244.55   $244.60  
  Purchase #3 $7.31   7.795%   $7.8798   $7.88   $7.90   $7.90  
  Purchase #4 $223.28   7.293%   $239.5638   $239.56   $239.55   $239.60  
  Purchase #5 $133.27   13.532%   $151.3041   $151.30   $151.30   $151.30  
  Purchase #6 $57.25   11.537%   $63.8549   $63.85   $63.85   $63.90  
  Purchase #7 $28.67   8.838%   $31.2039   $31.20   $31.20   $31.20  
  7 purchase totals = $755.21       $833.6144   $833.60   $833.60   $833.80