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 $219.64   12.199%   $246.4339   $246.43   $246.45   $246.40  
  Purchase #2 $103.73   8.262%   $112.3002   $112.30   $112.30   $112.30  
  Purchase #3 $213.32   6.129%   $226.3944   $226.39   $226.40   $226.40  
  Purchase #4 $171.97   11.848%   $192.345   $192.35   $192.35   $192.30  
  Purchase #5 $28.93   6.700%   $30.8683   $30.87   $30.85   $30.90  
  Purchase #6 $45.46   9.771%   $49.9019   $49.90   $49.90   $49.90  
  Purchase #7 $42.89   8.777%   $46.6545   $46.65   $46.65   $46.70  
  7 purchase totals = $825.94       $904.8982   $904.89   $904.90   $904.90