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 $213.53   9.682%   $234.204   $234.20   $234.20   $234.20  
  Purchase #2 $234.68   7.241%   $251.6732   $251.67   $251.65   $251.70  
  Purchase #3 $73.81   13.658%   $83.891   $83.89   $83.90   $83.90  
  Purchase #4 $194.80   9.555%   $213.4131   $213.41   $213.40   $213.40  
  Purchase #5 $118.41   9.799%   $130.013   $130.01   $130.00   $130.00  
  Purchase #6 $182.57   12.595%   $205.5647   $205.56   $205.55   $205.60  
  Purchase #7 $209.28   10.309%   $230.8547   $230.85   $230.85   $230.90  
  7 purchase totals = $1,227.08       $1,349.6137   $1,349.59   $1,349.55   $1,349.70