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 $206.33   13.210%   $233.5862   $233.59   $233.60   $233.60  
  Purchase #2 $21.99   9.217%   $24.0168   $24.02   $24.00   $24.00  
  Purchase #3 $110.92   9.833%   $121.8268   $121.83   $121.85   $121.80  
  Purchase #4 $176.39   5.275%   $185.6946   $185.69   $185.70   $185.70  
  Purchase #5 $144.83   12.183%   $162.4746   $162.47   $162.45   $162.50  
  Purchase #6 $177.94   5.367%   $187.49   $187.49   $187.50   $187.50  
  Purchase #7 $109.77   6.817%   $117.253   $117.25   $117.25   $117.30  
  7 purchase totals = $948.17       $1,032.3420   $1,032.34   $1,032.35   $1,032.40