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 $217.87   13.630%   $247.5657   $247.57   $247.55   $247.60  
  Purchase #2 $156.91   8.148%   $169.695   $169.70   $169.70   $169.70  
  Purchase #3 $79.68   5.154%   $83.7867   $83.79   $83.80   $83.80  
  Purchase #4 $143.92   9.150%   $157.0887   $157.09   $157.10   $157.10  
  Purchase #5 $199.80   11.285%   $222.3474   $222.35   $222.35   $222.30  
  Purchase #6 $134.80   8.787%   $146.6449   $146.64   $146.65   $146.60  
  Purchase #7 $185.25   9.332%   $202.5375   $202.54   $202.55   $202.50  
  7 purchase totals = $1,118.23       $1,229.6659   $1,229.68   $1,229.70   $1,229.60