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 $155.33   12.202%   $174.2834   $174.28   $174.30   $174.30  
  Purchase #2 $14.35   5.822%   $15.1855   $15.19   $15.20   $15.20  
  Purchase #3 $62.91   12.572%   $70.819   $70.82   $70.80   $70.80  
  Purchase #4 $208.85   5.552%   $220.4454   $220.45   $220.45   $220.40  
  Purchase #5 $231.63   13.774%   $263.5347   $263.53   $263.55   $263.50  
  Purchase #6 $31.38   12.414%   $35.2755   $35.28   $35.30   $35.30  
  Purchase #7 $156.70   5.112%   $164.7105   $164.71   $164.70   $164.70  
  7 purchase totals = $861.15       $944.2540   $944.26   $944.30   $944.20