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 $71.40   8.721%   $77.6268   $77.63   $77.65   $77.60  
  Purchase #2 $202.71   9.644%   $222.2594   $222.26   $222.25   $222.30  
  Purchase #3 $6.45   4.597%   $6.7465   $6.75   $6.75   $6.70  
  Purchase #4 $54.42   6.729%   $58.0819   $58.08   $58.10   $58.10  
  Purchase #5 $202.68   8.321%   $219.545   $219.55   $219.55   $219.50  
  Purchase #6 $244.32   6.426%   $260.02   $260.02   $260.00   $260.00  
  Purchase #7 $147.60   6.375%   $157.0095   $157.01   $157.00   $157.00  
  7 purchase totals = $929.58       $1,001.2891   $1,001.30   $1,001.30   $1,001.20