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 $216.29   9.278%   $236.3574   $236.36   $236.35   $236.40  
  Purchase #2 $34.46   13.669%   $39.1703   $39.17   $39.15   $39.20  
  Purchase #3 $172.51   6.636%   $183.9578   $183.96   $183.95   $184.00  
  Purchase #4 $167.57   13.641%   $190.4282   $190.43   $190.45   $190.40  
  Purchase #5 $109.58   9.436%   $119.92   $119.92   $119.90   $119.90  
  Purchase #6 $247.81   13.232%   $280.6002   $280.60   $280.60   $280.60  
  Purchase #7 $230.95   5.405%   $243.4328   $243.43   $243.45   $243.40  
  7 purchase totals = $1,179.17       $1,293.8667   $1,293.87   $1,293.85   $1,293.90