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 $174.61   6.526%   $186.005   $186.01   $186.00   $186.00  
  Purchase #2 $91.69   7.599%   $98.6575   $98.66   $98.65   $98.70  
  Purchase #3 $199.84   5.600%   $211.031   $211.03   $211.05   $211.00  
  Purchase #4 $68.25   10.433%   $75.3705   $75.37   $75.35   $75.40  
  Purchase #5 $15.37   3.506%   $15.9089   $15.91   $15.90   $15.90  
  Purchase #6 $154.51   13.416%   $175.2391   $175.24   $175.25   $175.20  
  Purchase #7 $189.94   4.174%   $197.8681   $197.87   $197.85   $197.90  
  7 purchase totals = $894.21       $960.0801   $960.09   $960.05   $960.10