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 $226.60   11.110%   $251.7753   $251.78   $251.80   $251.80  
  Purchase #2 $100.33   13.115%   $113.4883   $113.49   $113.50   $113.50  
  Purchase #3 $99.49   5.767%   $105.2276   $105.23   $105.25   $105.20  
  Purchase #4 $219.90   3.409%   $227.3964   $227.40   $227.40   $227.40  
  Purchase #5 $188.97   12.681%   $212.9333   $212.93   $212.95   $212.90  
  Purchase #6 $33.81   3.289%   $34.922   $34.92   $34.90   $34.90  
  Purchase #7 $92.93   6.232%   $98.7214   $98.72   $98.70   $98.70  
  7 purchase totals = $962.03       $1,044.4643   $1,044.47   $1,044.50   $1,044.40