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 $211.34   9.654%   $231.7428   $231.74   $231.75   $231.70  
  Purchase #2 $161.41   6.834%   $172.4408   $172.44   $172.45   $172.40  
  Purchase #3 $216.25   12.249%   $242.7385   $242.74   $242.75   $242.70  
  Purchase #4 $229.50   7.582%   $246.9007   $246.90   $246.90   $246.90  
  Purchase #5 $160.95   13.370%   $182.469   $182.47   $182.45   $182.50  
  Purchase #6 $179.85   4.491%   $187.9271   $187.93   $187.95   $187.90  
  Purchase #7 $47.92   11.816%   $53.5822   $53.58   $53.60   $53.60  
  7 purchase totals = $1,207.22       $1,317.8011   $1,317.80   $1,317.85   $1,317.70