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 $231.64   12.244%   $260.002   $260.00   $260.00   $260.00  
  Purchase #2 $107.78   7.732%   $116.1135   $116.11   $116.10   $116.10  
  Purchase #3 $26.59   4.447%   $27.7725   $27.77   $27.75   $27.80  
  Purchase #4 $45.47   3.422%   $47.026   $47.03   $47.05   $47.00  
  Purchase #5 $50.85   11.288%   $56.5899   $56.59   $56.60   $56.60  
  Purchase #6 $184.77   13.161%   $209.0876   $209.09   $209.10   $209.10  
  Purchase #7 $246.93   12.110%   $276.8332   $276.83   $276.85   $276.80  
  7 purchase totals = $894.03       $993.4247   $993.42   $993.45   $993.40