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 $189.31   13.322%   $214.5299   $214.53   $214.55   $214.50  
  Purchase #2 $108.25   12.106%   $121.3547   $121.35   $121.35   $121.40  
  Purchase #3 $167.95   10.357%   $185.3446   $185.34   $185.35   $185.30  
  Purchase #4 $240.59   9.447%   $263.3185   $263.32   $263.30   $263.30  
  Purchase #5 $133.57   9.659%   $146.4715   $146.47   $146.45   $146.50  
  Purchase #6 $83.98   13.691%   $95.4777   $95.48   $95.50   $95.50  
  Purchase #7 $146.62   13.155%   $165.9079   $165.91   $165.90   $165.90  
  7 purchase totals = $1,070.27       $1,192.4048   $1,192.40   $1,192.40   $1,192.40