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 $227.76   9.206%   $248.7276   $248.73   $248.75   $248.70  
  Purchase #2 $205.56   8.302%   $222.6256   $222.63   $222.65   $222.60  
  Purchase #3 $228.78   9.708%   $250.99   $250.99   $251.00   $251.00  
  Purchase #4 $19.70   6.518%   $20.984   $20.98   $21.00   $21.00  
  Purchase #5 $226.98   3.244%   $234.3432   $234.34   $234.35   $234.30  
  Purchase #6 $243.99   12.247%   $273.8715   $273.87   $273.85   $273.90  
  Purchase #7 $67.87   11.367%   $75.5848   $75.58   $75.60   $75.60  
  7 purchase totals = $1,220.64       $1,327.1267   $1,327.12   $1,327.20   $1,327.10