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 $167.66   9.122%   $182.9539   $182.95   $182.95   $183.00  
  Purchase #2 $249.56   6.561%   $265.9336   $265.93   $265.95   $265.90  
  Purchase #3 $110.92   5.709%   $117.2524   $117.25   $117.25   $117.30  
  Purchase #4 $244.47   10.299%   $269.648   $269.65   $269.65   $269.60  
  Purchase #5 $38.31   9.697%   $42.0249   $42.02   $42.00   $42.00  
  Purchase #6 $240.57   7.603%   $258.8605   $258.86   $258.85   $258.90  
  Purchase #7 $205.47   12.639%   $231.4394   $231.44   $231.45   $231.40  
  7 purchase totals = $1,256.96       $1,368.1127   $1,368.10   $1,368.10   $1,368.10