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 $93.39   5.370%   $98.405   $98.41   $98.40   $98.40  
  Purchase #2 $152.33   5.197%   $160.2466   $160.25   $160.25   $160.20  
  Purchase #3 $173.25   11.158%   $192.5812   $192.58   $192.60   $192.60  
  Purchase #4 $171.43   7.823%   $184.841   $184.84   $184.85   $184.80  
  Purchase #5 $158.44   9.427%   $173.3761   $173.38   $173.40   $173.40  
  Purchase #6 $44.47   9.688%   $48.7783   $48.78   $48.80   $48.80  
  Purchase #7 $72.97   5.501%   $76.9841   $76.98   $77.00   $77.00  
  7 purchase totals = $866.28       $935.2123   $935.22   $935.30   $935.20