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 $54.28   8.738%   $59.023   $59.02   $59.00   $59.00  
  Purchase #2 $201.97   13.206%   $228.6422   $228.64   $228.65   $228.60  
  Purchase #3 $18.53   7.551%   $19.9292   $19.93   $19.95   $19.90  
  Purchase #4 $49.72   13.286%   $56.3258   $56.33   $56.35   $56.30  
  Purchase #5 $38.96   9.521%   $42.6694   $42.67   $42.65   $42.70  
  Purchase #6 $180.26   11.854%   $201.628   $201.63   $201.65   $201.60  
  Purchase #7 $225.41   10.172%   $248.3387   $248.34   $248.35   $248.30  
  7 purchase totals = $769.13       $856.5563   $856.56   $856.60   $856.40