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 $234.32   4.832%   $245.6423   $245.64   $245.65   $245.60  
  Purchase #2 $168.46   4.677%   $176.3389   $176.34   $176.35   $176.30  
  Purchase #3 $85.98   12.112%   $96.3939   $96.39   $96.40   $96.40  
  Purchase #4 $26.86   12.692%   $30.2691   $30.27   $30.25   $30.30  
  Purchase #5 $201.79   8.525%   $218.9926   $218.99   $219.00   $219.00  
  Purchase #6 $73.41   8.709%   $79.8033   $79.80   $79.80   $79.80  
  Purchase #7 $173.43   10.146%   $191.0262   $191.03   $191.05   $191.00  
  7 purchase totals = $964.25       $1,038.4663   $1,038.46   $1,038.50   $1,038.40