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 $56.79   11.339%   $63.2294   $63.23   $63.25   $63.20  
  Purchase #2 $48.58   10.599%   $53.729   $53.73   $53.75   $53.70  
  Purchase #3 $214.65   12.434%   $241.3396   $241.34   $241.35   $241.30  
  Purchase #4 $102.87   10.256%   $113.4203   $113.42   $113.40   $113.40  
  Purchase #5 $199.44   8.518%   $216.4283   $216.43   $216.45   $216.40  
  Purchase #6 $229.30   12.838%   $258.7375   $258.74   $258.75   $258.70  
  Purchase #7 $62.37   3.769%   $64.7207   $64.72   $64.70   $64.70  
  7 purchase totals = $914.00       $1,011.6048   $1,011.61   $1,011.65   $1,011.40