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 $58.98   11.544%   $65.7887   $65.79   $65.80   $65.80  
  Purchase #2 $162.59   8.321%   $176.1191   $176.12   $176.10   $176.10  
  Purchase #3 $191.63   10.121%   $211.0249   $211.02   $211.00   $211.00  
  Purchase #4 $217.77   7.363%   $233.8044   $233.80   $233.80   $233.80  
  Purchase #5 $42.78   3.862%   $44.4322   $44.43   $44.45   $44.40  
  Purchase #6 $145.71   6.559%   $155.2671   $155.27   $155.25   $155.30  
  Purchase #7 $164.55   11.339%   $183.2083   $183.21   $183.20   $183.20  
  7 purchase totals = $984.01       $1,069.6447   $1,069.64   $1,069.60   $1,069.60