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 $141.88   11.624%   $158.3721   $158.37   $158.35   $158.40  
  Purchase #2 $155.76   4.303%   $162.4624   $162.46   $162.45   $162.50  
  Purchase #3 $44.80   9.148%   $48.8983   $48.90   $48.90   $48.90  
  Purchase #4 $138.46   4.863%   $145.1933   $145.19   $145.20   $145.20  
  Purchase #5 $237.43   12.273%   $266.5698   $266.57   $266.55   $266.60  
  Purchase #6 $35.70   10.765%   $39.5431   $39.54   $39.55   $39.50  
  Purchase #7 $170.58   13.159%   $193.0266   $193.03   $193.05   $193.00  
  7 purchase totals = $924.61       $1,014.0656   $1,014.06   $1,014.05   $1,014.10