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 $149.97   11.388%   $167.0486   $167.05   $167.05   $167.00  
  Purchase #2 $181.59   8.288%   $196.6402   $196.64   $196.65   $196.60  
  Purchase #3 $235.75   11.502%   $262.866   $262.87   $262.85   $262.90  
  Purchase #4 $116.68   7.102%   $124.9666   $124.97   $124.95   $125.00  
  Purchase #5 $247.98   12.291%   $278.4592   $278.46   $278.45   $278.50  
  Purchase #6 $176.29   13.812%   $200.6392   $200.64   $200.65   $200.60  
  Purchase #7 $22.35   11.748%   $24.9757   $24.98   $25.00   $25.00  
  7 purchase totals = $1,130.61       $1,255.5955   $1,255.61   $1,255.60   $1,255.60