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 $154.45   8.717%   $167.9134   $167.91   $167.90   $167.90  
  Purchase #2 $92.87   3.227%   $95.8669   $95.87   $95.85   $95.90  
  Purchase #3 $183.63   7.537%   $197.4702   $197.47   $197.45   $197.50  
  Purchase #4 $215.90   6.558%   $230.0587   $230.06   $230.05   $230.10  
  Purchase #5 $199.52   3.744%   $206.99   $206.99   $207.00   $207.00  
  Purchase #6 $178.47   9.376%   $195.2033   $195.20   $195.20   $195.20  
  Purchase #7 $228.48   5.281%   $240.546   $240.55   $240.55   $240.50  
  7 purchase totals = $1,253.32       $1,334.0485   $1,334.05   $1,334.00   $1,334.10