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 $58.66   8.385%   $63.5786   $63.58   $63.60   $63.60  
  Purchase #2 $156.93   4.280%   $163.6466   $163.65   $163.65   $163.60  
  Purchase #3 $208.93   8.346%   $226.3673   $226.37   $226.35   $226.40  
  Purchase #4 $208.29   4.104%   $216.8382   $216.84   $216.85   $216.80  
  Purchase #5 $84.55   10.717%   $93.6112   $93.61   $93.60   $93.60  
  Purchase #6 $230.73   4.525%   $241.1705   $241.17   $241.15   $241.20  
  Purchase #7 $231.49   13.501%   $262.7435   $262.74   $262.75   $262.70  
  7 purchase totals = $1,179.58       $1,267.9559   $1,267.96   $1,267.95   $1,267.90