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 $62.86   11.131%   $69.8569   $69.86   $69.85   $69.90  
  Purchase #2 $165.53   11.270%   $184.1852   $184.19   $184.20   $184.20  
  Purchase #3 $242.95   12.508%   $273.3382   $273.34   $273.35   $273.30  
  Purchase #4 $127.54   3.503%   $132.0077   $132.01   $132.00   $132.00  
  Purchase #5 $176.98   8.287%   $191.6463   $191.65   $191.65   $191.60  
  Purchase #6 $139.61   4.375%   $145.7179   $145.72   $145.70   $145.70  
  Purchase #7 $213.38   6.211%   $226.633   $226.63   $226.65   $226.60  
  7 purchase totals = $1,128.85       $1,223.3852   $1,223.40   $1,223.40   $1,223.30