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 $165.95   8.460%   $179.9894   $179.99   $180.00   $180.00  
  Purchase #2 $170.65   5.840%   $180.616   $180.62   $180.60   $180.60  
  Purchase #3 $175.92   7.470%   $189.0612   $189.06   $189.05   $189.10  
  Purchase #4 $210.60   10.740%   $233.2184   $233.22   $233.20   $233.20  
  Purchase #5 $121.37   9.516%   $132.9196   $132.92   $132.90   $132.90  
  Purchase #6 $48.51   7.655%   $52.2234   $52.22   $52.20   $52.20  
  Purchase #7 $164.28   7.725%   $176.9706   $176.97   $176.95   $177.00  
  7 purchase totals = $1,057.28       $1,144.9986   $1,145.00   $1,144.90   $1,145.00