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 $87.31   10.166%   $96.1859   $96.19   $96.20   $96.20  
  Purchase #2 $247.57   8.767%   $269.2745   $269.27   $269.25   $269.30  
  Purchase #3 $173.66   9.438%   $190.05   $190.05   $190.05   $190.10  
  Purchase #4 $177.78   12.713%   $200.3812   $200.38   $200.40   $200.40  
  Purchase #5 $184.30   7.210%   $197.588   $197.59   $197.60   $197.60  
  Purchase #6 $172.62   9.798%   $189.5333   $189.53   $189.55   $189.50  
  Purchase #7 $240.98   13.618%   $273.7967   $273.80   $273.80   $273.80  
  7 purchase totals = $1,284.22       $1,416.8096   $1,416.81   $1,416.85   $1,416.90