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 $102.46   11.715%   $114.4632   $114.46   $114.45   $114.50  
  Purchase #2 $229.77   6.816%   $245.4311   $245.43   $245.45   $245.40  
  Purchase #3 $121.95   5.473%   $128.6243   $128.62   $128.60   $128.60  
  Purchase #4 $245.77   12.620%   $276.7862   $276.79   $276.80   $276.80  
  Purchase #5 $207.41   6.506%   $220.9041   $220.90   $220.90   $220.90  
  Purchase #6 $169.64   5.194%   $178.4511   $178.45   $178.45   $178.50  
  Purchase #7 $238.56   12.862%   $269.2436   $269.24   $269.25   $269.20  
  7 purchase totals = $1,315.56       $1,433.9036   $1,433.89   $1,433.90   $1,433.90