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 $125.97   9.336%   $137.7306   $137.73   $137.75   $137.70  
  Purchase #2 $150.67   10.709%   $166.8053   $166.81   $166.80   $166.80  
  Purchase #3 $190.66   7.569%   $205.0911   $205.09   $205.10   $205.10  
  Purchase #4 $79.43   8.504%   $86.1847   $86.18   $86.20   $86.20  
  Purchase #5 $32.95   13.855%   $37.5152   $37.52   $37.50   $37.50  
  Purchase #6 $205.64   8.855%   $223.8494   $223.85   $223.85   $223.80  
  Purchase #7 $156.80   8.220%   $169.689   $169.69   $169.70   $169.70  
  7 purchase totals = $942.12       $1,026.8653   $1,026.87   $1,026.90   $1,026.80