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 $67.84   11.408%   $75.5792   $75.58   $75.60   $75.60  
  Purchase #2 $32.56   6.851%   $34.7907   $34.79   $34.80   $34.80  
  Purchase #3 $246.69   6.326%   $262.2956   $262.30   $262.30   $262.30  
  Purchase #4 $201.81   13.641%   $229.3389   $229.34   $229.35   $229.30  
  Purchase #5 $163.50   4.116%   $170.2297   $170.23   $170.25   $170.20  
  Purchase #6 $94.72   13.765%   $107.7582   $107.76   $107.75   $107.80  
  Purchase #7 $155.63   13.206%   $176.1825   $176.18   $176.20   $176.20  
  7 purchase totals = $962.75       $1,056.1748   $1,056.18   $1,056.25   $1,056.20