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 $245.35   11.276%   $273.0157   $273.02   $273.00   $273.00  
  Purchase #2 $149.91   13.190%   $169.6831   $169.68   $169.70   $169.70  
  Purchase #3 $77.34   6.462%   $82.3377   $82.34   $82.35   $82.30  
  Purchase #4 $106.45   9.147%   $116.187   $116.19   $116.20   $116.20  
  Purchase #5 $225.30   3.755%   $233.76   $233.76   $233.75   $233.80  
  Purchase #6 $167.62   4.461%   $175.0975   $175.10   $175.10   $175.10  
  Purchase #7 $24.58   6.734%   $26.2352   $26.24   $26.25   $26.20  
  7 purchase totals = $996.55       $1,076.3162   $1,076.33   $1,076.35   $1,076.30