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 $120.78   11.136%   $134.2301   $134.23   $134.25   $134.20  
  Purchase #2 $186.98   8.214%   $202.3385   $202.34   $202.35   $202.30  
  Purchase #3 $65.33   4.102%   $68.0098   $68.01   $68.00   $68.00  
  Purchase #4 $97.99   5.606%   $103.4833   $103.48   $103.50   $103.50  
  Purchase #5 $213.97   7.663%   $230.3665   $230.37   $230.35   $230.40  
  Purchase #6 $5.86   4.438%   $6.1201   $6.12   $6.10   $6.10  
  Purchase #7 $89.77   10.579%   $99.2668   $99.27   $99.25   $99.30  
  7 purchase totals = $780.68       $843.8151   $843.82   $843.80   $843.80