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 $84.99   12.605%   $95.703   $95.70   $95.70   $95.70  
  Purchase #2 $25.33   12.851%   $28.5852   $28.59   $28.60   $28.60  
  Purchase #3 $162.44   11.868%   $181.7184   $181.72   $181.70   $181.70  
  Purchase #4 $189.86   8.759%   $206.4898   $206.49   $206.50   $206.50  
  Purchase #5 $144.55   7.453%   $155.3233   $155.32   $155.30   $155.30  
  Purchase #6 $231.78   10.139%   $255.2802   $255.28   $255.30   $255.30  
  Purchase #7 $117.59   13.272%   $133.1965   $133.20   $133.20   $133.20  
  7 purchase totals = $956.54       $1,056.2964   $1,056.30   $1,056.30   $1,056.30