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 $234.39   13.309%   $265.585   $265.59   $265.60   $265.60  
  Purchase #2 $87.93   9.538%   $96.3168   $96.32   $96.30   $96.30  
  Purchase #3 $52.66   11.596%   $58.7665   $58.77   $58.75   $58.80  
  Purchase #4 $71.51   11.247%   $79.5527   $79.55   $79.55   $79.60  
  Purchase #5 $47.57   11.861%   $53.2123   $53.21   $53.20   $53.20  
  Purchase #6 $53.84   9.729%   $59.0781   $59.08   $59.10   $59.10  
  Purchase #7 $147.88   5.485%   $155.9912   $155.99   $156.00   $156.00  
  7 purchase totals = $695.78       $768.5026   $768.51   $768.50   $768.60