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 $106.26   12.581%   $119.6286   $119.63   $119.65   $119.60  
  Purchase #2 $138.50   6.543%   $147.5621   $147.56   $147.55   $147.60  
  Purchase #3 $111.32   13.865%   $126.7545   $126.75   $126.75   $126.80  
  Purchase #4 $73.53   12.107%   $82.4323   $82.43   $82.45   $82.40  
  Purchase #5 $86.46   9.282%   $94.4852   $94.49   $94.50   $94.50  
  Purchase #6 $241.42   8.631%   $262.257   $262.26   $262.25   $262.30  
  Purchase #7 $71.96   11.795%   $80.4477   $80.45   $80.45   $80.40  
  7 purchase totals = $829.45       $913.5674   $913.57   $913.60   $913.60