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 $164.64   11.310%   $183.2608   $183.26   $183.25   $183.30  
  Purchase #2 $216.46   8.662%   $235.2098   $235.21   $235.20   $235.20  
  Purchase #3 $198.46   4.350%   $207.093   $207.09   $207.10   $207.10  
  Purchase #4 $92.86   7.133%   $99.4837   $99.48   $99.50   $99.50  
  Purchase #5 $211.40   4.627%   $221.1815   $221.18   $221.20   $221.20  
  Purchase #6 $203.91   12.224%   $228.836   $228.84   $228.85   $228.80  
  Purchase #7 $11.93   13.182%   $13.5026   $13.50   $13.50   $13.50  
  7 purchase totals = $1,099.66       $1,188.5674   $1,188.56   $1,188.60   $1,188.60