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 $34.84   11.348%   $38.7936   $38.79   $38.80   $38.80  
  Purchase #2 $55.67   12.688%   $62.7334   $62.73   $62.75   $62.70  
  Purchase #3 $65.97   4.533%   $68.9604   $68.96   $68.95   $69.00  
  Purchase #4 $118.94   3.729%   $123.3753   $123.38   $123.40   $123.40  
  Purchase #5 $130.61   11.139%   $145.1586   $145.16   $145.15   $145.20  
  Purchase #6 $211.58   12.610%   $238.2602   $238.26   $238.25   $238.30  
  Purchase #7 $80.55   5.212%   $84.7483   $84.75   $84.75   $84.70  
  7 purchase totals = $698.16       $762.0298   $762.03   $762.05   $762.10