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 $169.97   13.454%   $192.8378   $192.84   $192.85   $192.80  
  Purchase #2 $64.48   13.627%   $73.2667   $73.27   $73.25   $73.30  
  Purchase #3 $216.77   11.133%   $240.903   $240.90   $240.90   $240.90  
  Purchase #4 $209.57   11.139%   $232.914   $232.91   $232.90   $232.90  
  Purchase #5 $201.65   11.688%   $225.2189   $225.22   $225.20   $225.20  
  Purchase #6 $74.87   4.346%   $78.1239   $78.12   $78.10   $78.10  
  Purchase #7 $43.92   5.426%   $46.3031   $46.30   $46.30   $46.30  
  7 purchase totals = $981.23       $1,089.5674   $1,089.56   $1,089.50   $1,089.50