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 $67.43   9.610%   $73.91   $73.91   $73.90   $73.90  
  Purchase #2 $183.79   9.266%   $200.82   $200.82   $200.80   $200.80  
  Purchase #3 $168.93   6.830%   $180.4679   $180.47   $180.45   $180.50  
  Purchase #4 $207.28   8.407%   $224.706   $224.71   $224.70   $224.70  
  Purchase #5 $112.42   12.188%   $126.1217   $126.12   $126.10   $126.10  
  Purchase #6 $191.29   6.233%   $203.2131   $203.21   $203.20   $203.20  
  Purchase #7 $145.51   8.282%   $157.5611   $157.56   $157.55   $157.60  
  7 purchase totals = $1,076.65       $1,166.7998   $1,166.80   $1,166.70   $1,166.80