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 $58.39   13.638%   $66.3532   $66.35   $66.35   $66.40  
  Purchase #2 $134.97   12.862%   $152.3298   $152.33   $152.35   $152.30  
  Purchase #3 $188.93   13.578%   $214.5829   $214.58   $214.60   $214.60  
  Purchase #4 $162.47   4.689%   $170.0882   $170.09   $170.10   $170.10  
  Purchase #5 $214.86   5.464%   $226.6   $226.60   $226.60   $226.60  
  Purchase #6 $203.97   7.639%   $219.5513   $219.55   $219.55   $219.60  
  Purchase #7 $81.40   10.151%   $89.6629   $89.66   $89.65   $89.70  
  7 purchase totals = $1,044.99       $1,139.1683   $1,139.16   $1,139.20   $1,139.30