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 $183.84   5.608%   $194.1497   $194.15   $194.15   $194.10  
  Purchase #2 $67.62   11.280%   $75.2475   $75.25   $75.25   $75.20  
  Purchase #3 $204.82   7.493%   $220.1672   $220.17   $220.15   $220.20  
  Purchase #4 $249.95   9.368%   $273.3653   $273.37   $273.35   $273.40  
  Purchase #5 $94.30   12.299%   $105.898   $105.90   $105.90   $105.90  
  Purchase #6 $158.65   13.409%   $179.9234   $179.92   $179.90   $179.90  
  Purchase #7 $94.72   9.104%   $103.3433   $103.34   $103.35   $103.30  
  7 purchase totals = $1,053.90       $1,152.0944   $1,152.10   $1,152.05   $1,152.00