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 $119.72   10.530%   $132.3265   $132.33   $132.35   $132.30  
  Purchase #2 $115.52   9.171%   $126.1143   $126.11   $126.10   $126.10  
  Purchase #3 $162.58   6.796%   $173.6289   $173.63   $173.65   $173.60  
  Purchase #4 $52.37   8.746%   $56.9503   $56.95   $56.95   $57.00  
  Purchase #5 $237.98   13.323%   $269.6861   $269.69   $269.70   $269.70  
  Purchase #6 $238.34   8.290%   $258.0984   $258.10   $258.10   $258.10  
  Purchase #7 $206.94   3.751%   $214.7023   $214.70   $214.70   $214.70  
  7 purchase totals = $1,133.45       $1,231.5068   $1,231.51   $1,231.55   $1,231.50