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 $92.53   3.751%   $96.0008   $96.00   $96.00   $96.00  
  Purchase #2 $219.40   12.589%   $247.0203   $247.02   $247.00   $247.00  
  Purchase #3 $78.74   7.176%   $84.3904   $84.39   $84.40   $84.40  
  Purchase #4 $130.89   11.350%   $145.746   $145.75   $145.75   $145.70  
  Purchase #5 $89.45   10.182%   $98.5578   $98.56   $98.55   $98.60  
  Purchase #6 $124.72   5.242%   $131.2578   $131.26   $131.25   $131.30  
  Purchase #7 $51.72   5.839%   $54.7399   $54.74   $54.75   $54.70  
  7 purchase totals = $787.45       $857.7130   $857.72   $857.70   $857.70