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 $44.67   13.479%   $50.6911   $50.69   $50.70   $50.70  
  Purchase #2 $211.75   10.490%   $233.9626   $233.96   $233.95   $234.00  
  Purchase #3 $223.57   13.451%   $253.6424   $253.64   $253.65   $253.60  
  Purchase #4 $92.34   9.839%   $101.4253   $101.43   $101.45   $101.40  
  Purchase #5 $244.85   5.102%   $257.3422   $257.34   $257.35   $257.30  
  Purchase #6 $188.59   4.358%   $196.8088   $196.81   $196.80   $196.80  
  Purchase #7 $9.76   13.530%   $11.0805   $11.08   $11.10   $11.10  
  7 purchase totals = $1,015.53       $1,104.9529   $1,104.95   $1,105.00   $1,104.90