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 $83.57   11.270%   $92.9883   $92.99   $93.00   $93.00  
  Purchase #2 $246.32   8.412%   $267.0404   $267.04   $267.05   $267.00  
  Purchase #3 $124.46   6.510%   $132.5623   $132.56   $132.55   $132.60  
  Purchase #4 $24.86   12.479%   $27.9623   $27.96   $27.95   $28.00  
  Purchase #5 $78.34   11.375%   $87.2512   $87.25   $87.25   $87.30  
  Purchase #6 $27.90   3.469%   $28.8679   $28.87   $28.85   $28.90  
  Purchase #7 $196.85   9.422%   $215.3972   $215.40   $215.40   $215.40  
  7 purchase totals = $782.30       $852.0696   $852.07   $852.05   $852.20