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 $68.33   8.864%   $74.3868   $74.39   $74.40   $74.40  
  Purchase #2 $200.92   6.482%   $213.9436   $213.94   $213.95   $213.90  
  Purchase #3 $159.33   11.428%   $177.5382   $177.54   $177.55   $177.50  
  Purchase #4 $236.29   7.466%   $253.9314   $253.93   $253.95   $253.90  
  Purchase #5 $59.33   4.510%   $62.0058   $62.01   $62.00   $62.00  
  Purchase #6 $185.92   3.640%   $192.6875   $192.69   $192.70   $192.70  
  Purchase #7 $66.91   13.199%   $75.7415   $75.74   $75.75   $75.70  
  7 purchase totals = $977.03       $1,050.2348   $1,050.24   $1,050.30   $1,050.10