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 $224.89   12.634%   $253.3026   $253.30   $253.30   $253.30  
  Purchase #2 $184.41   11.693%   $205.9731   $205.97   $205.95   $206.00  
  Purchase #3 $232.45   9.349%   $254.1818   $254.18   $254.20   $254.20  
  Purchase #4 $12.99   12.248%   $14.581   $14.58   $14.60   $14.60  
  Purchase #5 $125.33   10.456%   $138.4345   $138.43   $138.45   $138.40  
  Purchase #6 $136.37   11.546%   $152.1153   $152.12   $152.10   $152.10  
  Purchase #7 $80.81   6.540%   $86.095   $86.10   $86.10   $86.10  
  7 purchase totals = $997.25       $1,104.6833   $1,104.68   $1,104.70   $1,104.70