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 $89.44   5.448%   $94.3127   $94.31   $94.30   $94.30  
  Purchase #2 $112.80   4.486%   $117.8602   $117.86   $117.85   $117.90  
  Purchase #3 $196.54   8.841%   $213.9161   $213.92   $213.90   $213.90  
  Purchase #4 $238.83   9.364%   $261.194   $261.19   $261.20   $261.20  
  Purchase #5 $68.77   6.288%   $73.0943   $73.09   $73.10   $73.10  
  Purchase #6 $52.52   5.118%   $55.208   $55.21   $55.20   $55.20  
  Purchase #7 $23.54   9.708%   $25.8253   $25.83   $25.85   $25.80  
  7 purchase totals = $782.44       $841.4106   $841.41   $841.40   $841.40