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 $124.67   13.472%   $141.4655   $141.47   $141.45   $141.50  
  Purchase #2 $68.74   11.552%   $76.6808   $76.68   $76.70   $76.70  
  Purchase #3 $104.97   8.189%   $113.566   $113.57   $113.55   $113.60  
  Purchase #4 $213.88   8.573%   $232.2159   $232.22   $232.20   $232.20  
  Purchase #5 $109.67   4.479%   $114.5821   $114.58   $114.60   $114.60  
  Purchase #6 $162.84   8.735%   $177.0641   $177.06   $177.05   $177.10  
  Purchase #7 $194.28   8.430%   $210.6578   $210.66   $210.65   $210.70  
  7 purchase totals = $979.05       $1,066.2322   $1,066.24   $1,066.20   $1,066.40