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 $48.89   4.116%   $50.9023   $50.90   $50.90   $50.90  
  Purchase #2 $197.86   6.641%   $210.9999   $211.00   $211.00   $211.00  
  Purchase #3 $130.81   4.616%   $136.8482   $136.85   $136.85   $136.80  
  Purchase #4 $162.78   3.154%   $167.9141   $167.91   $167.90   $167.90  
  Purchase #5 $218.33   9.858%   $239.853   $239.85   $239.85   $239.90  
  Purchase #6 $235.59   10.606%   $260.5767   $260.58   $260.60   $260.60  
  Purchase #7 $165.42   3.495%   $171.2014   $171.20   $171.20   $171.20  
  7 purchase totals = $1,159.68       $1,238.2956   $1,238.29   $1,238.30   $1,238.30