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 $87.90   5.740%   $92.9455   $92.95   $92.95   $92.90  
  Purchase #2 $44.40   7.177%   $47.5866   $47.59   $47.60   $47.60  
  Purchase #3 $191.56   6.494%   $203.9999   $204.00   $204.00   $204.00  
  Purchase #4 $218.47   6.214%   $232.0457   $232.05   $232.05   $232.00  
  Purchase #5 $137.52   12.429%   $154.6124   $154.61   $154.60   $154.60  
  Purchase #6 $116.93   4.508%   $122.2012   $122.20   $122.20   $122.20  
  Purchase #7 $106.94   11.365%   $119.0937   $119.09   $119.10   $119.10  
  7 purchase totals = $903.72       $972.4850   $972.49   $972.50   $972.40