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 $245.58   9.430%   $268.7382   $268.74   $268.75   $268.70  
  Purchase #2 $189.38   4.743%   $198.3623   $198.36   $198.35   $198.40  
  Purchase #3 $104.47   13.513%   $118.587   $118.59   $118.60   $118.60  
  Purchase #4 $184.70   5.580%   $195.0063   $195.01   $195.00   $195.00  
  Purchase #5 $235.31   11.191%   $261.6435   $261.64   $261.65   $261.60  
  Purchase #6 $58.29   8.493%   $63.2406   $63.24   $63.25   $63.20  
  Purchase #7 $48.36   3.629%   $50.115   $50.12   $50.10   $50.10  
  7 purchase totals = $1,066.09       $1,155.6929   $1,155.70   $1,155.70   $1,155.60