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 $66.64   10.677%   $73.7552   $73.76   $73.75   $73.80  
  Purchase #2 $219.82   5.443%   $231.7848   $231.78   $231.80   $231.80  
  Purchase #3 $23.67   12.343%   $26.5916   $26.59   $26.60   $26.60  
  Purchase #4 $195.95   13.761%   $222.9147   $222.91   $222.90   $222.90  
  Purchase #5 $192.36   9.802%   $211.2151   $211.22   $211.20   $211.20  
  Purchase #6 $145.36   4.749%   $152.2631   $152.26   $152.25   $152.30  
  Purchase #7 $29.61   5.580%   $31.2622   $31.26   $31.25   $31.30  
  7 purchase totals = $873.41       $949.7867   $949.78   $949.75   $949.90