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 $216.44   4.860%   $226.959   $226.96   $226.95   $227.00  
  Purchase #2 $229.30   13.737%   $260.7989   $260.80   $260.80   $260.80  
  Purchase #3 $24.57   4.469%   $25.668   $25.67   $25.65   $25.70  
  Purchase #4 $33.76   5.724%   $35.6924   $35.69   $35.70   $35.70  
  Purchase #5 $14.55   4.815%   $15.2506   $15.25   $15.25   $15.30  
  Purchase #6 $129.57   9.251%   $141.5565   $141.56   $141.55   $141.60  
  Purchase #7 $230.51   4.482%   $240.8415   $240.84   $240.85   $240.80  
  7 purchase totals = $878.70       $946.7669   $946.77   $946.75   $946.90