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 $61.35   3.178%   $63.2997   $63.30   $63.30   $63.30  
  Purchase #2 $9.42   6.524%   $10.0346   $10.03   $10.05   $10.00  
  Purchase #3 $199.29   11.106%   $221.4231   $221.42   $221.40   $221.40  
  Purchase #4 $120.44   12.803%   $135.8599   $135.86   $135.85   $135.90  
  Purchase #5 $162.35   4.845%   $170.2159   $170.22   $170.20   $170.20  
  Purchase #6 $174.72   6.711%   $186.4455   $186.45   $186.45   $186.40  
  Purchase #7 $165.33   6.592%   $176.2286   $176.23   $176.25   $176.20  
  7 purchase totals = $892.90       $963.5073   $963.51   $963.50   $963.40