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 $90.57   11.853%   $101.3053   $101.31   $101.30   $101.30  
  Purchase #2 $176.77   12.555%   $198.9635   $198.96   $198.95   $199.00  
  Purchase #3 $155.64   9.790%   $170.8772   $170.88   $170.90   $170.90  
  Purchase #4 $11.49   4.586%   $12.0169   $12.02   $12.00   $12.00  
  Purchase #5 $237.28   10.569%   $262.3581   $262.36   $262.35   $262.40  
  Purchase #6 $173.63   10.241%   $191.4114   $191.41   $191.40   $191.40  
  Purchase #7 $59.91   6.112%   $63.5717   $63.57   $63.55   $63.60  
  7 purchase totals = $905.29       $1,000.5041   $1,000.51   $1,000.45   $1,000.60