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 $57.88   4.638%   $60.5645   $60.56   $60.55   $60.60  
  Purchase #2 $173.56   8.728%   $188.7083   $188.71   $188.70   $188.70  
  Purchase #3 $228.53   3.321%   $236.1195   $236.12   $236.10   $236.10  
  Purchase #4 $210.52   11.610%   $234.9614   $234.96   $234.95   $235.00  
  Purchase #5 $186.75   12.506%   $210.105   $210.11   $210.10   $210.10  
  Purchase #6 $81.34   7.662%   $87.5723   $87.57   $87.55   $87.60  
  Purchase #7 $54.56   6.104%   $57.8903   $57.89   $57.90   $57.90  
  7 purchase totals = $993.14       $1,075.9213   $1,075.92   $1,075.85   $1,076.00