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 $38.58   11.691%   $43.0904   $43.09   $43.10   $43.10  
  Purchase #2 $224.93   8.176%   $243.3203   $243.32   $243.30   $243.30  
  Purchase #3 $63.86   11.200%   $71.0123   $71.01   $71.00   $71.00  
  Purchase #4 $202.37   8.341%   $219.2497   $219.25   $219.25   $219.20  
  Purchase #5 $189.82   4.448%   $198.2632   $198.26   $198.25   $198.30  
  Purchase #6 $163.49   11.442%   $182.1965   $182.20   $182.20   $182.20  
  Purchase #7 $62.84   3.419%   $64.9885   $64.99   $65.00   $65.00  
  7 purchase totals = $945.89       $1,022.1209   $1,022.12   $1,022.10   $1,022.10