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 $202.42   5.729%   $214.0166   $214.02   $214.00   $214.00  
  Purchase #2 $23.46   13.811%   $26.7001   $26.70   $26.70   $26.70  
  Purchase #3 $60.81   13.238%   $68.86   $68.86   $68.85   $68.90  
  Purchase #4 $230.84   12.381%   $259.4203   $259.42   $259.40   $259.40  
  Purchase #5 $144.99   9.874%   $159.3063   $159.31   $159.30   $159.30  
  Purchase #6 $45.29   5.458%   $47.7619   $47.76   $47.75   $47.80  
  Purchase #7 $67.46   6.495%   $71.8415   $71.84   $71.85   $71.80  
  7 purchase totals = $775.27       $847.9067   $847.91   $847.85   $847.90