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 $49.25   11.816%   $55.0694   $55.07   $55.05   $55.10  
  Purchase #2 $142.76   4.871%   $149.7138   $149.71   $149.70   $149.70  
  Purchase #3 $84.69   8.135%   $91.5795   $91.58   $91.60   $91.60  
  Purchase #4 $224.87   3.560%   $232.8754   $232.88   $232.90   $232.90  
  Purchase #5 $95.89   8.151%   $103.706   $103.71   $103.70   $103.70  
  Purchase #6 $134.80   13.263%   $152.6785   $152.68   $152.70   $152.70  
  Purchase #7 $62.30   11.654%   $69.5604   $69.56   $69.55   $69.60  
  7 purchase totals = $794.56       $855.1830   $855.19   $855.20   $855.30