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 $244.60   8.403%   $265.1537   $265.15   $265.15   $265.20  
  Purchase #2 $224.53   7.347%   $241.0262   $241.03   $241.05   $241.00  
  Purchase #3 $75.36   7.845%   $81.272   $81.27   $81.25   $81.30  
  Purchase #4 $116.57   6.686%   $124.3639   $124.36   $124.35   $124.40  
  Purchase #5 $84.43   10.777%   $93.529   $93.53   $93.55   $93.50  
  Purchase #6 $149.42   7.216%   $160.2021   $160.20   $160.20   $160.20  
  Purchase #7 $208.42   4.586%   $217.9781   $217.98   $218.00   $218.00  
  7 purchase totals = $1,103.33       $1,183.5250   $1,183.52   $1,183.55   $1,183.60