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 $146.35   10.378%   $161.5382   $161.54   $161.55   $161.50  
  Purchase #2 $232.29   7.430%   $249.5491   $249.55   $249.55   $249.50  
  Purchase #3 $94.37   10.718%   $104.4846   $104.48   $104.50   $104.50  
  Purchase #4 $53.44   4.155%   $55.6604   $55.66   $55.65   $55.70  
  Purchase #5 $190.62   13.651%   $216.6415   $216.64   $216.65   $216.60  
  Purchase #6 $203.53   11.816%   $227.5791   $227.58   $227.60   $227.60  
  Purchase #7 $44.76   7.380%   $48.0633   $48.06   $48.05   $48.10  
  7 purchase totals = $965.36       $1,063.5162   $1,063.51   $1,063.55   $1,063.50