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 $61.87   4.775%   $64.8243   $64.82   $64.80   $64.80  
  Purchase #2 $244.60   7.274%   $262.3922   $262.39   $262.40   $262.40  
  Purchase #3 $175.34   13.240%   $198.555   $198.56   $198.55   $198.60  
  Purchase #4 $99.93   13.753%   $113.6734   $113.67   $113.65   $113.70  
  Purchase #5 $236.42   13.516%   $268.3745   $268.37   $268.35   $268.40  
  Purchase #6 $204.71   3.184%   $211.228   $211.23   $211.25   $211.20  
  Purchase #7 $40.90   5.510%   $43.1536   $43.15   $43.15   $43.20  
  7 purchase totals = $1,063.77       $1,162.2010   $1,162.19   $1,162.15   $1,162.30