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 $104.42   9.744%   $114.5947   $114.59   $114.60   $114.60  
  Purchase #2 $195.53   8.813%   $212.7621   $212.76   $212.75   $212.80  
  Purchase #3 $11.58   12.159%   $12.988   $12.99   $13.00   $13.00  
  Purchase #4 $97.27   7.695%   $104.7549   $104.75   $104.75   $104.80  
  Purchase #5 $81.50   8.244%   $88.2189   $88.22   $88.20   $88.20  
  Purchase #6 $246.51   11.194%   $274.1043   $274.10   $274.10   $274.10  
  Purchase #7 $180.75   13.861%   $205.8038   $205.80   $205.80   $205.80  
  7 purchase totals = $917.56       $1,013.2267   $1,013.21   $1,013.20   $1,013.30