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 $67.34   13.261%   $76.27   $76.27   $76.25   $76.30  
  Purchase #2 $236.60   13.287%   $268.037   $268.04   $268.05   $268.00  
  Purchase #3 $163.92   11.224%   $182.3184   $182.32   $182.30   $182.30  
  Purchase #4 $58.27   12.750%   $65.6994   $65.70   $65.70   $65.70  
  Purchase #5 $105.41   11.767%   $117.8136   $117.81   $117.80   $117.80  
  Purchase #6 $186.35   9.356%   $203.7849   $203.78   $203.80   $203.80  
  Purchase #7 $169.60   3.834%   $176.1025   $176.10   $176.10   $176.10  
  7 purchase totals = $987.49       $1,090.0258   $1,090.02   $1,090.00   $1,090.00