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 $118.66   11.821%   $132.6868   $132.69   $132.70   $132.70  
  Purchase #2 $52.88   12.128%   $59.2933   $59.29   $59.30   $59.30  
  Purchase #3 $154.31   12.156%   $173.0679   $173.07   $173.05   $173.10  
  Purchase #4 $185.97   9.807%   $204.2081   $204.21   $204.20   $204.20  
  Purchase #5 $138.88   8.161%   $150.214   $150.21   $150.20   $150.20  
  Purchase #6 $154.69   6.542%   $164.8098   $164.81   $164.80   $164.80  
  Purchase #7 $126.92   5.267%   $133.6049   $133.60   $133.60   $133.60  
  7 purchase totals = $932.31       $1,017.8848   $1,017.88   $1,017.85   $1,017.90