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 $161.80   7.650%   $174.1777   $174.18   $174.20   $174.20  
  Purchase #2 $77.62   11.306%   $86.3957   $86.40   $86.40   $86.40  
  Purchase #3 $119.34   13.723%   $135.717   $135.72   $135.70   $135.70  
  Purchase #4 $148.55   9.722%   $162.992   $162.99   $163.00   $163.00  
  Purchase #5 $60.55   10.701%   $67.0295   $67.03   $67.05   $67.00  
  Purchase #6 $202.84   11.647%   $226.4648   $226.46   $226.45   $226.50  
  Purchase #7 $49.97   10.306%   $55.1199   $55.12   $55.10   $55.10  
  7 purchase totals = $820.67       $907.8966   $907.90   $907.90   $907.90