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 $111.73   12.578%   $125.7834   $125.78   $125.80   $125.80  
  Purchase #2 $192.47   8.417%   $208.6702   $208.67   $208.65   $208.70  
  Purchase #3 $237.88   12.732%   $268.1669   $268.17   $268.15   $268.20  
  Purchase #4 $160.27   8.212%   $173.4314   $173.43   $173.45   $173.40  
  Purchase #5 $86.34   9.194%   $94.2781   $94.28   $94.30   $94.30  
  Purchase #6 $145.48   6.339%   $154.702   $154.70   $154.70   $154.70  
  Purchase #7 $19.39   9.777%   $21.2858   $21.29   $21.30   $21.30  
  7 purchase totals = $953.56       $1,046.3178   $1,046.32   $1,046.35   $1,046.40