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 $210.25   7.484%   $225.9851   $225.99   $226.00   $226.00  
  Purchase #2 $100.96   10.116%   $111.1731   $111.17   $111.15   $111.20  
  Purchase #3 $246.32   9.206%   $268.9962   $269.00   $269.00   $269.00  
  Purchase #4 $86.46   11.496%   $96.3994   $96.40   $96.40   $96.40  
  Purchase #5 $23.47   6.424%   $24.9777   $24.98   $25.00   $25.00  
  Purchase #6 $61.34   5.808%   $64.9026   $64.90   $64.90   $64.90  
  Purchase #7 $228.90   13.481%   $259.758   $259.76   $259.75   $259.80  
  7 purchase totals = $957.70       $1,052.1921   $1,052.20   $1,052.20   $1,052.30