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 $105.61   3.310%   $109.1057   $109.11   $109.10   $109.10  
  Purchase #2 $104.95   13.241%   $118.8464   $118.85   $118.85   $118.80  
  Purchase #3 $70.48   6.356%   $74.9597   $74.96   $74.95   $75.00  
  Purchase #4 $202.35   10.493%   $223.5826   $223.58   $223.60   $223.60  
  Purchase #5 $40.49   12.745%   $45.6505   $45.65   $45.65   $45.70  
  Purchase #6 $178.90   5.643%   $188.9953   $189.00   $189.00   $189.00  
  Purchase #7 $69.49   10.528%   $76.8059   $76.81   $76.80   $76.80  
  7 purchase totals = $772.27       $837.9461   $837.96   $837.95   $838.00