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 $97.51   10.247%   $107.5018   $107.50   $107.50   $107.50  
  Purchase #2 $237.74   9.760%   $260.9434   $260.94   $260.95   $260.90  
  Purchase #3 $163.25   5.259%   $171.8353   $171.84   $171.85   $171.80  
  Purchase #4 $61.98   9.147%   $67.6493   $67.65   $67.65   $67.60  
  Purchase #5 $153.77   6.669%   $164.0249   $164.02   $164.00   $164.00  
  Purchase #6 $229.97   13.240%   $260.418   $260.42   $260.40   $260.40  
  Purchase #7 $220.78   12.261%   $247.8498   $247.85   $247.85   $247.80  
  7 purchase totals = $1,165.00       $1,280.2225   $1,280.22   $1,280.20   $1,280.00