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 $32.98   4.822%   $34.5703   $34.57   $34.55   $34.60  
  Purchase #2 $8.81   7.155%   $9.4404   $9.44   $9.45   $9.40  
  Purchase #3 $118.76   10.816%   $131.6051   $131.61   $131.60   $131.60  
  Purchase #4 $248.92   5.668%   $263.0288   $263.03   $263.05   $263.00  
  Purchase #5 $192.77   6.213%   $204.7468   $204.75   $204.75   $204.70  
  Purchase #6 $69.64   9.870%   $76.5135   $76.51   $76.50   $76.50  
  Purchase #7 $157.64   11.609%   $175.9404   $175.94   $175.95   $175.90  
  7 purchase totals = $829.52       $895.8453   $895.85   $895.85   $895.70