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 $151.79   11.348%   $169.0151   $169.02   $169.00   $169.00  
  Purchase #2 $156.32   12.430%   $175.7506   $175.75   $175.75   $175.80  
  Purchase #3 $201.99   8.782%   $219.7288   $219.73   $219.75   $219.70  
  Purchase #4 $144.87   4.544%   $151.4529   $151.45   $151.45   $151.50  
  Purchase #5 $245.96   11.392%   $273.9798   $273.98   $274.00   $274.00  
  Purchase #6 $196.46   4.658%   $205.6111   $205.61   $205.60   $205.60  
  Purchase #7 $138.66   7.574%   $149.1621   $149.16   $149.15   $149.20  
  7 purchase totals = $1,236.05       $1,344.7004   $1,344.70   $1,344.70   $1,344.80