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 $32.63   7.153%   $34.964   $34.96   $34.95   $35.00  
  Purchase #2 $106.48   5.774%   $112.6282   $112.63   $112.65   $112.60  
  Purchase #3 $67.82   11.452%   $75.5867   $75.59   $75.60   $75.60  
  Purchase #4 $111.62   9.352%   $122.0587   $122.06   $122.05   $122.10  
  Purchase #5 $239.53   5.362%   $252.3736   $252.37   $252.35   $252.40  
  Purchase #6 $58.69   3.198%   $60.5669   $60.57   $60.55   $60.60  
  Purchase #7 $244.99   8.408%   $265.5888   $265.59   $265.60   $265.60  
  7 purchase totals = $861.76       $923.7669   $923.77   $923.75   $923.90