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 $154.77   9.368%   $169.2689   $169.27   $169.25   $169.30  
  Purchase #2 $33.41   7.778%   $36.0086   $36.01   $36.00   $36.00  
  Purchase #3 $183.43   8.353%   $198.7519   $198.75   $198.75   $198.80  
  Purchase #4 $241.78   3.836%   $251.0547   $251.05   $251.05   $251.10  
  Purchase #5 $192.92   4.631%   $201.8541   $201.85   $201.85   $201.90  
  Purchase #6 $238.64   11.577%   $266.2674   $266.27   $266.25   $266.30  
  Purchase #7 $226.65   8.257%   $245.3645   $245.36   $245.35   $245.40  
  7 purchase totals = $1,271.60       $1,368.5701   $1,368.56   $1,368.50   $1,368.80