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 $178.86   10.292%   $197.2683   $197.27   $197.25   $197.30  
  Purchase #2 $115.35   9.765%   $126.6139   $126.61   $126.60   $126.60  
  Purchase #3 $189.84   8.233%   $205.4695   $205.47   $205.45   $205.50  
  Purchase #4 $32.42   9.707%   $35.567   $35.57   $35.55   $35.60  
  Purchase #5 $62.26   10.537%   $68.8203   $68.82   $68.80   $68.80  
  Purchase #6 $186.83   7.737%   $201.285   $201.29   $201.30   $201.30  
  Purchase #7 $29.62   12.284%   $33.2585   $33.26   $33.25   $33.30  
  7 purchase totals = $795.18       $868.2825   $868.29   $868.20   $868.40