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 $8.78   9.119%   $9.5806   $9.58   $9.60   $9.60  
  Purchase #2 $191.91   7.615%   $206.5239   $206.52   $206.50   $206.50  
  Purchase #3 $246.56   4.571%   $257.8303   $257.83   $257.85   $257.80  
  Purchase #4 $23.54   9.767%   $25.8392   $25.84   $25.85   $25.80  
  Purchase #5 $137.92   11.208%   $153.3781   $153.38   $153.40   $153.40  
  Purchase #6 $76.33   12.740%   $86.0544   $86.05   $86.05   $86.10  
  Purchase #7 $81.28   4.214%   $84.7051   $84.71   $84.70   $84.70  
  7 purchase totals = $766.32       $823.9116   $823.91   $823.95   $823.90