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 $231.47   5.637%   $244.518   $244.52   $244.50   $244.50  
  Purchase #2 $87.91   5.440%   $92.6923   $92.69   $92.70   $92.70  
  Purchase #3 $214.76   10.801%   $237.9562   $237.96   $237.95   $238.00  
  Purchase #4 $115.52   10.506%   $127.6565   $127.66   $127.65   $127.70  
  Purchase #5 $164.90   8.307%   $178.5982   $178.60   $178.60   $178.60  
  Purchase #6 $179.82   13.399%   $203.9141   $203.91   $203.90   $203.90  
  Purchase #7 $89.68   3.823%   $93.1085   $93.11   $93.10   $93.10  
  7 purchase totals = $1,084.06       $1,178.4438   $1,178.45   $1,178.40   $1,178.50