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 $232.90   6.544%   $248.141   $248.14   $248.15   $248.10  
  Purchase #2 $33.84   4.336%   $35.3073   $35.31   $35.30   $35.30  
  Purchase #3 $19.52   3.219%   $20.1483   $20.15   $20.15   $20.10  
  Purchase #4 $120.50   8.177%   $130.3533   $130.35   $130.35   $130.40  
  Purchase #5 $147.49   5.617%   $155.7745   $155.77   $155.75   $155.80  
  Purchase #6 $189.34   8.514%   $205.4604   $205.46   $205.45   $205.50  
  Purchase #7 $199.75   12.205%   $224.1295   $224.13   $224.15   $224.10  
  7 purchase totals = $943.34       $1,019.3143   $1,019.31   $1,019.30   $1,019.30