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 $42.49   9.635%   $46.5839   $46.58   $46.60   $46.60  
  Purchase #2 $244.42   13.286%   $276.8936   $276.89   $276.90   $276.90  
  Purchase #3 $164.54   4.205%   $171.4589   $171.46   $171.45   $171.50  
  Purchase #4 $61.27   5.485%   $64.6307   $64.63   $64.65   $64.60  
  Purchase #5 $226.80   3.308%   $234.3025   $234.30   $234.30   $234.30  
  Purchase #6 $142.94   12.133%   $160.2829   $160.28   $160.30   $160.30  
  Purchase #7 $57.91   3.605%   $59.9977   $60.00   $60.00   $60.00  
  7 purchase totals = $940.37       $1,014.1502   $1,014.14   $1,014.20   $1,014.20