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 $59.98   5.225%   $63.114   $63.11   $63.10   $63.10  
  Purchase #2 $79.79   5.157%   $83.9048   $83.90   $83.90   $83.90  
  Purchase #3 $152.61   12.704%   $171.9976   $172.00   $172.00   $172.00  
  Purchase #4 $174.36   11.658%   $194.6869   $194.69   $194.70   $194.70  
  Purchase #5 $54.95   10.595%   $60.772   $60.77   $60.75   $60.80  
  Purchase #6 $126.53   5.712%   $133.7574   $133.76   $133.75   $133.80  
  Purchase #7 $90.41   8.317%   $97.9294   $97.93   $97.95   $97.90  
  7 purchase totals = $738.63       $806.1621   $806.16   $806.15   $806.20