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 $44.93   12.361%   $50.4838   $50.48   $50.50   $50.50  
  Purchase #2 $120.40   11.319%   $134.0281   $134.03   $134.05   $134.00  
  Purchase #3 $149.32   9.202%   $163.0604   $163.06   $163.05   $163.10  
  Purchase #4 $220.71   6.475%   $235.001   $235.00   $235.00   $235.00  
  Purchase #5 $93.58   12.861%   $105.6153   $105.62   $105.60   $105.60  
  Purchase #6 $144.49   10.751%   $160.0241   $160.02   $160.00   $160.00  
  Purchase #7 $242.32   4.295%   $252.7276   $252.73   $252.75   $252.70  
  7 purchase totals = $1,015.75       $1,100.9403   $1,100.94   $1,100.95   $1,100.90