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 $209.65   4.817%   $219.7488   $219.75   $219.75   $219.70  
  Purchase #2 $46.37   6.593%   $49.4272   $49.43   $49.45   $49.40  
  Purchase #3 $233.85   4.248%   $243.7839   $243.78   $243.80   $243.80  
  Purchase #4 $225.77   5.533%   $238.2619   $238.26   $238.25   $238.30  
  Purchase #5 $153.69   12.332%   $172.6431   $172.64   $172.65   $172.60  
  Purchase #6 $26.93   9.233%   $29.4164   $29.42   $29.40   $29.40  
  Purchase #7 $97.84   8.430%   $106.0879   $106.09   $106.10   $106.10  
  7 purchase totals = $994.10       $1,059.3692   $1,059.37   $1,059.40   $1,059.30