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 $213.41   6.179%   $226.5966   $226.60   $226.60   $226.60  
  Purchase #2 $94.52   5.463%   $99.6836   $99.68   $99.70   $99.70  
  Purchase #3 $31.27   8.523%   $33.9351   $33.94   $33.95   $33.90  
  Purchase #4 $166.75   11.441%   $185.8279   $185.83   $185.85   $185.80  
  Purchase #5 $217.97   10.475%   $240.8024   $240.80   $240.80   $240.80  
  Purchase #6 $206.90   11.191%   $230.0542   $230.05   $230.05   $230.10  
  Purchase #7 $233.58   13.537%   $265.1997   $265.20   $265.20   $265.20  
  7 purchase totals = $1,164.40       $1,282.0995   $1,282.10   $1,282.15   $1,282.10