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 $231.48   12.338%   $260.04   $260.04   $260.05   $260.00  
  Purchase #2 $53.29   12.222%   $59.8031   $59.80   $59.80   $59.80  
  Purchase #3 $83.36   4.174%   $86.8394   $86.84   $86.85   $86.80  
  Purchase #4 $77.27   6.672%   $82.4255   $82.43   $82.45   $82.40  
  Purchase #5 $84.66   13.621%   $96.1915   $96.19   $96.20   $96.20  
  Purchase #6 $25.28   10.154%   $27.8469   $27.85   $27.85   $27.80  
  Purchase #7 $239.99   3.376%   $248.0921   $248.09   $248.10   $248.10  
  7 purchase totals = $795.33       $861.2385   $861.24   $861.30   $861.10