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 $86.77   9.631%   $95.1268   $95.13   $95.15   $95.10  
  Purchase #2 $14.33   3.421%   $14.8202   $14.82   $14.80   $14.80  
  Purchase #3 $81.45   12.467%   $91.6044   $91.60   $91.60   $91.60  
  Purchase #4 $60.85   5.292%   $64.0702   $64.07   $64.05   $64.10  
  Purchase #5 $127.92   7.537%   $137.5613   $137.56   $137.55   $137.60  
  Purchase #6 $175.70   4.449%   $183.5169   $183.52   $183.50   $183.50  
  Purchase #7 $10.68   4.674%   $11.1792   $11.18   $11.20   $11.20  
  7 purchase totals = $557.70       $597.8790   $597.88   $597.85   $597.90