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 $57.42   9.718%   $63.0001   $63.00   $63.00   $63.00  
  Purchase #2 $176.59   8.653%   $191.8703   $191.87   $191.85   $191.90  
  Purchase #3 $80.80   4.632%   $84.5427   $84.54   $84.55   $84.50  
  Purchase #4 $177.66   3.103%   $183.1728   $183.17   $183.15   $183.20  
  Purchase #5 $233.96   8.815%   $254.5836   $254.58   $254.60   $254.60  
  Purchase #6 $200.66   5.692%   $212.0816   $212.08   $212.10   $212.10  
  Purchase #7 $168.51   10.613%   $186.394   $186.39   $186.40   $186.40  
  7 purchase totals = $1,095.60       $1,175.6451   $1,175.63   $1,175.65   $1,175.70