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 $40.42   10.571%   $44.6928   $44.69   $44.70   $44.70  
  Purchase #2 $250.33   10.226%   $275.9287   $275.93   $275.95   $275.90  
  Purchase #3 $152.94   8.870%   $166.5058   $166.51   $166.50   $166.50  
  Purchase #4 $34.62   6.113%   $36.7363   $36.74   $36.75   $36.70  
  Purchase #5 $169.63   6.816%   $181.192   $181.19   $181.20   $181.20  
  Purchase #6 $238.28   5.771%   $252.0311   $252.03   $252.05   $252.00  
  Purchase #7 $33.33   5.740%   $35.2431   $35.24   $35.25   $35.20  
  7 purchase totals = $919.55       $992.3298   $992.33   $992.40   $992.20