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 $62.68   4.839%   $65.7131   $65.71   $65.70   $65.70  
  Purchase #2 $120.39   8.816%   $131.0036   $131.00   $131.00   $131.00  
  Purchase #3 $174.43   4.793%   $182.7904   $182.79   $182.80   $182.80  
  Purchase #4 $191.26   13.266%   $216.6326   $216.63   $216.65   $216.60  
  Purchase #5 $130.43   3.445%   $134.9233   $134.92   $134.90   $134.90  
  Purchase #6 $106.35   6.704%   $113.4797   $113.48   $113.50   $113.50  
  Purchase #7 $12.76   11.733%   $14.2571   $14.26   $14.25   $14.30  
  7 purchase totals = $798.30       $858.7998   $858.79   $858.80   $858.80