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 $57.53   10.523%   $63.5839   $63.58   $63.60   $63.60  
  Purchase #2 $95.40   7.322%   $102.3852   $102.39   $102.40   $102.40  
  Purchase #3 $31.79   12.621%   $35.8022   $35.80   $35.80   $35.80  
  Purchase #4 $114.55   6.167%   $121.6143   $121.61   $121.60   $121.60  
  Purchase #5 $81.92   6.769%   $87.4652   $87.47   $87.45   $87.50  
  Purchase #6 $228.92   7.629%   $246.3843   $246.38   $246.40   $246.40  
  Purchase #7 $62.37   11.773%   $69.7128   $69.71   $69.70   $69.70  
  7 purchase totals = $672.48       $726.9479   $726.94   $726.95   $727.00