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 $212.47   6.709%   $226.7246   $226.72   $226.70   $226.70  
  Purchase #2 $157.83   3.687%   $163.6492   $163.65   $163.65   $163.60  
  Purchase #3 $60.48   6.637%   $64.4941   $64.49   $64.50   $64.50  
  Purchase #4 $112.45   13.400%   $127.5183   $127.52   $127.50   $127.50  
  Purchase #5 $161.80   4.157%   $168.526   $168.53   $168.55   $168.50  
  Purchase #6 $182.42   5.647%   $192.7213   $192.72   $192.70   $192.70  
  Purchase #7 $51.76   3.338%   $53.4877   $53.49   $53.50   $53.50  
  7 purchase totals = $939.21       $997.1212   $997.12   $997.10   $997.00