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 $233.80   6.820%   $249.7452   $249.75   $249.75   $249.70  
  Purchase #2 $41.46   8.345%   $44.9198   $44.92   $44.90   $44.90  
  Purchase #3 $33.59   3.447%   $34.7478   $34.75   $34.75   $34.70  
  Purchase #4 $168.66   9.154%   $184.0991   $184.10   $184.10   $184.10  
  Purchase #5 $117.49   11.707%   $131.2446   $131.24   $131.25   $131.20  
  Purchase #6 $217.61   6.108%   $230.9016   $230.90   $230.90   $230.90  
  Purchase #7 $232.94   4.459%   $243.3268   $243.33   $243.35   $243.30  
  7 purchase totals = $1,045.55       $1,118.9849   $1,118.99   $1,119.00   $1,118.80