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 $73.56   3.694%   $76.2773   $76.28   $76.30   $76.30  
  Purchase #2 $7.29   5.255%   $7.6731   $7.67   $7.65   $7.70  
  Purchase #3 $212.93   13.469%   $241.6095   $241.61   $241.60   $241.60  
  Purchase #4 $233.39   8.307%   $252.7777   $252.78   $252.80   $252.80  
  Purchase #5 $124.93   3.494%   $129.2951   $129.30   $129.30   $129.30  
  Purchase #6 $143.82   8.679%   $156.3021   $156.30   $156.30   $156.30  
  Purchase #7 $227.53   7.172%   $243.8485   $243.85   $243.85   $243.80  
  7 purchase totals = $1,023.45       $1,107.7833   $1,107.79   $1,107.80   $1,107.80