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 $67.77   4.266%   $70.6611   $70.66   $70.65   $70.70  
  Purchase #2 $235.76   11.864%   $263.7306   $263.73   $263.75   $263.70  
  Purchase #3 $179.32   13.466%   $203.4672   $203.47   $203.45   $203.50  
  Purchase #4 $230.84   6.194%   $245.1382   $245.14   $245.15   $245.10  
  Purchase #5 $55.60   6.532%   $59.2318   $59.23   $59.25   $59.20  
  Purchase #6 $201.58   9.241%   $220.208   $220.21   $220.20   $220.20  
  Purchase #7 $237.32   10.789%   $262.9245   $262.92   $262.90   $262.90  
  7 purchase totals = $1,208.19       $1,325.3614   $1,325.36   $1,325.35   $1,325.30