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 $59.25   11.610%   $66.1289   $66.13   $66.15   $66.10  
  Purchase #2 $73.53   6.236%   $78.1153   $78.12   $78.10   $78.10  
  Purchase #3 $186.70   7.258%   $200.2507   $200.25   $200.25   $200.30  
  Purchase #4 $202.57   5.595%   $213.9038   $213.90   $213.90   $213.90  
  Purchase #5 $41.32   9.611%   $45.2913   $45.29   $45.30   $45.30  
  Purchase #6 $229.69   13.652%   $261.0473   $261.05   $261.05   $261.00  
  Purchase #7 $186.58   4.337%   $194.672   $194.67   $194.65   $194.70  
  7 purchase totals = $979.64       $1,059.4093   $1,059.41   $1,059.40   $1,059.40