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 $63.32   13.189%   $71.6713   $71.67   $71.65   $71.70  
  Purchase #2 $239.37   5.782%   $253.2104   $253.21   $253.20   $253.20  
  Purchase #3 $85.87   9.728%   $94.2234   $94.22   $94.20   $94.20  
  Purchase #4 $170.66   8.363%   $184.9323   $184.93   $184.95   $184.90  
  Purchase #5 $11.43   5.402%   $12.0474   $12.05   $12.05   $12.00  
  Purchase #6 $87.85   5.351%   $92.5509   $92.55   $92.55   $92.60  
  Purchase #7 $245.89   3.272%   $253.9355   $253.94   $253.95   $253.90  
  7 purchase totals = $904.39       $962.5712   $962.57   $962.55   $962.50