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 $65.43   13.123%   $74.0164   $74.02   $74.00   $74.00  
  Purchase #2 $247.58   4.287%   $258.1938   $258.19   $258.20   $258.20  
  Purchase #3 $236.38   3.585%   $244.8542   $244.85   $244.85   $244.90  
  Purchase #4 $78.57   6.745%   $83.8695   $83.87   $83.85   $83.90  
  Purchase #5 $194.39   8.670%   $211.2436   $211.24   $211.25   $211.20  
  Purchase #6 $160.48   10.680%   $177.6193   $177.62   $177.60   $177.60  
  Purchase #7 $6.51   11.603%   $7.2654   $7.27   $7.25   $7.30  
  7 purchase totals = $989.34       $1,057.0622   $1,057.06   $1,057.00   $1,057.10