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 $212.72   10.787%   $235.6661   $235.67   $235.65   $235.70  
  Purchase #2 $45.83   3.433%   $47.4033   $47.40   $47.40   $47.40  
  Purchase #3 $116.42   6.164%   $123.5961   $123.60   $123.60   $123.60  
  Purchase #4 $33.83   7.640%   $36.4146   $36.41   $36.40   $36.40  
  Purchase #5 $149.40   3.439%   $154.5379   $154.54   $154.55   $154.50  
  Purchase #6 $204.34   4.255%   $213.0347   $213.03   $213.05   $213.00  
  Purchase #7 $123.37   12.662%   $138.9911   $138.99   $139.00   $139.00  
  7 purchase totals = $885.91       $949.6438   $949.64   $949.65   $949.60