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 $50.41   10.596%   $55.7514   $55.75   $55.75   $55.80  
  Purchase #2 $191.76   3.169%   $197.8369   $197.84   $197.85   $197.80  
  Purchase #3 $51.84   6.251%   $55.0805   $55.08   $55.10   $55.10  
  Purchase #4 $208.32   4.325%   $217.3298   $217.33   $217.35   $217.30  
  Purchase #5 $54.76   8.503%   $59.4162   $59.42   $59.40   $59.40  
  Purchase #6 $59.81   5.684%   $63.2096   $63.21   $63.20   $63.20  
  Purchase #7 $182.48   8.495%   $197.9817   $197.98   $198.00   $198.00  
  7 purchase totals = $799.38       $846.6061   $846.61   $846.65   $846.60