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 $236.57   11.300%   $263.3024   $263.30   $263.30   $263.30  
  Purchase #2 $56.25   10.297%   $62.0421   $62.04   $62.05   $62.00  
  Purchase #3 $176.81   11.834%   $197.7337   $197.73   $197.75   $197.70  
  Purchase #4 $242.34   4.128%   $252.3438   $252.34   $252.35   $252.30  
  Purchase #5 $115.52   8.776%   $125.658   $125.66   $125.65   $125.70  
  Purchase #6 $33.93   4.217%   $35.3608   $35.36   $35.35   $35.40  
  Purchase #7 $63.84   12.830%   $72.0307   $72.03   $72.05   $72.00  
  7 purchase totals = $925.26       $1,008.4715   $1,008.46   $1,008.50   $1,008.40