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 $154.36   12.457%   $173.5886   $173.59   $173.60   $173.60  
  Purchase #2 $227.45   4.667%   $238.0651   $238.07   $238.05   $238.10  
  Purchase #3 $186.35   8.171%   $201.5767   $201.58   $201.60   $201.60  
  Purchase #4 $157.94   13.127%   $178.6728   $178.67   $178.65   $178.70  
  Purchase #5 $193.28   4.225%   $201.4461   $201.45   $201.45   $201.40  
  Purchase #6 $148.39   3.363%   $153.3804   $153.38   $153.40   $153.40  
  Purchase #7 $114.37   4.125%   $119.0878   $119.09   $119.10   $119.10  
  7 purchase totals = $1,182.14       $1,265.8175   $1,265.83   $1,265.85   $1,265.90