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 $146.47   13.773%   $166.6433   $166.64   $166.65   $166.60  
  Purchase #2 $207.83   4.190%   $216.5381   $216.54   $216.55   $216.50  
  Purchase #3 $36.75   4.752%   $38.4964   $38.50   $38.50   $38.50  
  Purchase #4 $82.59   13.395%   $93.6529   $93.65   $93.65   $93.70  
  Purchase #5 $222.40   11.238%   $247.3933   $247.39   $247.40   $247.40  
  Purchase #6 $187.86   12.107%   $210.6042   $210.60   $210.60   $210.60  
  Purchase #7 $224.50   6.695%   $239.5303   $239.53   $239.55   $239.50  
  7 purchase totals = $1,108.40       $1,212.8585   $1,212.85   $1,212.90   $1,212.80