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 $47.64   12.538%   $53.6131   $53.61   $53.60   $53.60  
  Purchase #2 $128.79   4.692%   $134.8328   $134.83   $134.85   $134.80  
  Purchase #3 $63.39   5.326%   $66.7662   $66.77   $66.75   $66.80  
  Purchase #4 $182.61   10.768%   $202.2734   $202.27   $202.25   $202.30  
  Purchase #5 $69.74   10.856%   $77.311   $77.31   $77.30   $77.30  
  Purchase #6 $159.93   3.288%   $165.1885   $165.19   $165.20   $165.20  
  Purchase #7 $236.60   11.701%   $264.2846   $264.28   $264.30   $264.30  
  7 purchase totals = $888.70       $964.2696   $964.26   $964.25   $964.30