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 $228.99   3.263%   $236.4619   $236.46   $236.45   $236.50  
  Purchase #2 $94.69   13.280%   $107.2648   $107.26   $107.25   $107.30  
  Purchase #3 $49.29   13.581%   $55.9841   $55.98   $56.00   $56.00  
  Purchase #4 $61.79   4.757%   $64.7294   $64.73   $64.75   $64.70  
  Purchase #5 $241.79   9.406%   $264.5328   $264.53   $264.55   $264.50  
  Purchase #6 $70.71   6.158%   $75.0643   $75.06   $75.05   $75.10  
  Purchase #7 $168.49   11.333%   $187.585   $187.59   $187.60   $187.60  
  7 purchase totals = $915.75       $991.6223   $991.61   $991.65   $991.70