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 $213.25   13.829%   $242.7403   $242.74   $242.75   $242.70  
  Purchase #2 $54.42   9.635%   $59.6634   $59.66   $59.65   $59.70  
  Purchase #3 $179.87   12.198%   $201.8105   $201.81   $201.80   $201.80  
  Purchase #4 $224.97   9.263%   $245.809   $245.81   $245.80   $245.80  
  Purchase #5 $116.57   11.557%   $130.042   $130.04   $130.05   $130.00  
  Purchase #6 $108.61   13.639%   $123.4233   $123.42   $123.40   $123.40  
  Purchase #7 $13.63   5.834%   $14.4252   $14.43   $14.45   $14.40  
  7 purchase totals = $911.32       $1,017.9137   $1,017.91   $1,017.90   $1,017.80