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 $213.94   5.791%   $226.3293   $226.33   $226.35   $226.30  
  Purchase #2 $13.31   11.199%   $14.8006   $14.80   $14.80   $14.80  
  Purchase #3 $144.69   10.263%   $159.5395   $159.54   $159.55   $159.50  
  Purchase #4 $169.66   13.676%   $192.8627   $192.86   $192.85   $192.90  
  Purchase #5 $12.93   8.196%   $13.9897   $13.99   $14.00   $14.00  
  Purchase #6 $80.35   10.840%   $89.0599   $89.06   $89.05   $89.10  
  Purchase #7 $209.35   5.765%   $221.419   $221.42   $221.40   $221.40  
  7 purchase totals = $844.23       $918.0007   $918.00   $918.00   $918.00