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 $209.67   8.383%   $227.2466   $227.25   $227.25   $227.20  
  Purchase #2 $143.37   6.613%   $152.8511   $152.85   $152.85   $152.90  
  Purchase #3 $80.53   7.231%   $86.3531   $86.35   $86.35   $86.40  
  Purchase #4 $182.78   12.660%   $205.9199   $205.92   $205.90   $205.90  
  Purchase #5 $64.75   6.799%   $69.1524   $69.15   $69.15   $69.20  
  Purchase #6 $43.94   3.751%   $45.5882   $45.59   $45.60   $45.60  
  Purchase #7 $95.41   12.152%   $107.0042   $107.00   $107.00   $107.00  
  7 purchase totals = $820.45       $894.1155   $894.11   $894.10   $894.20