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 $73.44   12.561%   $82.6648   $82.66   $82.65   $82.70  
  Purchase #2 $49.87   10.295%   $55.0041   $55.00   $55.00   $55.00  
  Purchase #3 $157.70   8.299%   $170.7875   $170.79   $170.80   $170.80  
  Purchase #4 $198.25   5.804%   $209.7564   $209.76   $209.75   $209.80  
  Purchase #5 $245.71   11.253%   $273.3597   $273.36   $273.35   $273.40  
  Purchase #6 $221.58   8.744%   $240.955   $240.96   $240.95   $241.00  
  Purchase #7 $105.95   3.262%   $109.4061   $109.41   $109.40   $109.40  
  7 purchase totals = $1,052.50       $1,141.9336   $1,141.94   $1,141.90   $1,142.10