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 $108.97   8.127%   $117.826   $117.83   $117.85   $117.80  
  Purchase #2 $225.98   13.539%   $256.5754   $256.58   $256.60   $256.60  
  Purchase #3 $80.53   4.700%   $84.3149   $84.31   $84.30   $84.30  
  Purchase #4 $249.96   4.611%   $261.4857   $261.49   $261.50   $261.50  
  Purchase #5 $193.72   10.697%   $214.4422   $214.44   $214.45   $214.40  
  Purchase #6 $8.36   9.627%   $9.1648   $9.16   $9.15   $9.20  
  Purchase #7 $209.83   8.664%   $228.0097   $228.01   $228.00   $228.00  
  7 purchase totals = $1,077.35       $1,171.8187   $1,171.82   $1,171.85   $1,171.80