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 $174.58   13.335%   $197.8602   $197.86   $197.85   $197.90  
  Purchase #2 $77.61   3.661%   $80.4513   $80.45   $80.45   $80.50  
  Purchase #3 $238.47   10.473%   $263.445   $263.45   $263.45   $263.40  
  Purchase #4 $179.28   7.504%   $192.7332   $192.73   $192.75   $192.70  
  Purchase #5 $178.65   3.480%   $184.867   $184.87   $184.85   $184.90  
  Purchase #6 $240.71   11.531%   $268.4663   $268.47   $268.45   $268.50  
  Purchase #7 $81.68   5.778%   $86.3995   $86.40   $86.40   $86.40  
  7 purchase totals = $1,170.98       $1,274.2225   $1,274.23   $1,274.20   $1,274.30