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 $155.39   10.166%   $171.1869   $171.19   $171.20   $171.20  
  Purchase #2 $27.47   8.322%   $29.7561   $29.76   $29.75   $29.80  
  Purchase #3 $216.37   12.133%   $242.6222   $242.62   $242.60   $242.60  
  Purchase #4 $241.45   11.436%   $269.0622   $269.06   $269.05   $269.10  
  Purchase #5 $218.51   13.791%   $248.6447   $248.64   $248.65   $248.60  
  Purchase #6 $169.29   10.627%   $187.2804   $187.28   $187.30   $187.30  
  Purchase #7 $115.56   8.459%   $125.3352   $125.34   $125.35   $125.30  
  7 purchase totals = $1,144.04       $1,273.8877   $1,273.89   $1,273.90   $1,273.90