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 $61.80   3.268%   $63.8196   $63.82   $63.80   $63.80  
  Purchase #2 $218.58   3.242%   $225.6664   $225.67   $225.65   $225.70  
  Purchase #3 $47.39   7.308%   $50.8533   $50.85   $50.85   $50.90  
  Purchase #4 $198.96   13.595%   $226.0086   $226.01   $226.00   $226.00  
  Purchase #5 $141.64   4.864%   $148.5294   $148.53   $148.55   $148.50  
  Purchase #6 $184.26   5.626%   $194.6265   $194.63   $194.65   $194.60  
  Purchase #7 $173.95   6.574%   $185.3855   $185.39   $185.40   $185.40  
  7 purchase totals = $1,026.58       $1,094.8893   $1,094.90   $1,094.90   $1,094.90