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 $120.73   12.713%   $136.0784   $136.08   $136.10   $136.10  
  Purchase #2 $200.53   6.318%   $213.1995   $213.20   $213.20   $213.20  
  Purchase #3 $163.54   7.719%   $176.1637   $176.16   $176.15   $176.20  
  Purchase #4 $173.45   13.795%   $197.3774   $197.38   $197.40   $197.40  
  Purchase #5 $189.37   11.804%   $211.7232   $211.72   $211.70   $211.70  
  Purchase #6 $185.76   11.532%   $207.1818   $207.18   $207.20   $207.20  
  Purchase #7 $10.58   6.325%   $11.2492   $11.25   $11.25   $11.20  
  7 purchase totals = $1,043.96       $1,152.9732   $1,152.97   $1,153.00   $1,153.00