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 $150.26   11.279%   $167.2078   $167.21   $167.20   $167.20  
  Purchase #2 $211.77   9.731%   $232.3773   $232.38   $232.40   $232.40  
  Purchase #3 $246.42   9.342%   $269.4406   $269.44   $269.45   $269.40  
  Purchase #4 $232.40   11.340%   $258.7542   $258.75   $258.75   $258.80  
  Purchase #5 $166.68   3.380%   $172.3138   $172.31   $172.30   $172.30  
  Purchase #6 $134.63   3.525%   $139.3757   $139.38   $139.40   $139.40  
  Purchase #7 $163.65   4.777%   $171.4676   $171.47   $171.45   $171.50  
  7 purchase totals = $1,305.81       $1,410.9370   $1,410.94   $1,410.95   $1,411.00