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 $137.86   10.472%   $152.2967   $152.30   $152.30   $152.30  
  Purchase #2 $249.69   10.401%   $275.6603   $275.66   $275.65   $275.70  
  Purchase #3 $175.64   12.466%   $197.5353   $197.54   $197.55   $197.50  
  Purchase #4 $244.28   12.513%   $274.8468   $274.85   $274.85   $274.80  
  Purchase #5 $45.91   8.156%   $49.6544   $49.65   $49.65   $49.70  
  Purchase #6 $39.65   3.406%   $41.0005   $41.00   $41.00   $41.00  
  Purchase #7 $68.58   5.515%   $72.3622   $72.36   $72.35   $72.40  
  7 purchase totals = $961.61       $1,063.3562   $1,063.36   $1,063.35   $1,063.40