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 $69.88   5.286%   $73.5739   $73.57   $73.55   $73.60  
  Purchase #2 $58.28   4.538%   $60.9247   $60.92   $60.90   $60.90  
  Purchase #3 $129.97   7.839%   $140.1583   $140.16   $140.15   $140.20  
  Purchase #4 $78.67   3.408%   $81.3511   $81.35   $81.35   $81.40  
  Purchase #5 $133.78   10.283%   $147.5366   $147.54   $147.55   $147.50  
  Purchase #6 $122.59   3.251%   $126.5754   $126.58   $126.60   $126.60  
  Purchase #7 $65.78   8.432%   $71.3266   $71.33   $71.35   $71.30  
  7 purchase totals = $658.95       $701.4466   $701.45   $701.45   $701.50