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 $84.52   7.710%   $91.0365   $91.04   $91.05   $91.00  
  Purchase #2 $188.77   6.453%   $200.9513   $200.95   $200.95   $201.00  
  Purchase #3 $21.63   10.618%   $23.9267   $23.93   $23.95   $23.90  
  Purchase #4 $162.55   7.745%   $175.1395   $175.14   $175.15   $175.10  
  Purchase #5 $127.32   3.867%   $132.2435   $132.24   $132.25   $132.20  
  Purchase #6 $176.91   11.861%   $197.8933   $197.89   $197.90   $197.90  
  Purchase #7 $38.26   6.347%   $40.6884   $40.69   $40.70   $40.70  
  7 purchase totals = $799.96       $861.8792   $861.88   $861.95   $861.80