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 $24.61   6.840%   $26.2933   $26.29   $26.30   $26.30  
  Purchase #2 $117.94   3.164%   $121.6716   $121.67   $121.65   $121.70  
  Purchase #3 $145.72   5.394%   $153.5801   $153.58   $153.60   $153.60  
  Purchase #4 $118.79   6.145%   $126.0896   $126.09   $126.10   $126.10  
  Purchase #5 $208.61   12.584%   $234.8615   $234.86   $234.85   $234.90  
  Purchase #6 $197.89   9.203%   $216.1018   $216.10   $216.10   $216.10  
  Purchase #7 $56.59   4.305%   $59.0262   $59.03   $59.05   $59.00  
  7 purchase totals = $870.15       $937.6241   $937.62   $937.65   $937.70