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 $58.52   9.705%   $64.1994   $64.20   $64.20   $64.20  
  Purchase #2 $186.77   4.326%   $194.8497   $194.85   $194.85   $194.80  
  Purchase #3 $227.33   9.188%   $248.2171   $248.22   $248.20   $248.20  
  Purchase #4 $203.53   11.236%   $226.3986   $226.40   $226.40   $226.40  
  Purchase #5 $250.58   4.247%   $261.2221   $261.22   $261.20   $261.20  
  Purchase #6 $202.83   10.242%   $223.6038   $223.60   $223.60   $223.60  
  Purchase #7 $45.97   10.465%   $50.7808   $50.78   $50.80   $50.80  
  7 purchase totals = $1,175.53       $1,269.2715   $1,269.27   $1,269.25   $1,269.20