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 $54.90   9.252%   $59.9793   $59.98   $60.00   $60.00  
  Purchase #2 $11.33   8.212%   $12.2604   $12.26   $12.25   $12.30  
  Purchase #3 $214.91   12.629%   $242.051   $242.05   $242.05   $242.10  
  Purchase #4 $114.52   9.488%   $125.3857   $125.39   $125.40   $125.40  
  Purchase #5 $196.99   3.537%   $203.9575   $203.96   $203.95   $204.00  
  Purchase #6 $99.67   3.259%   $102.9182   $102.92   $102.90   $102.90  
  Purchase #7 $213.63   10.366%   $235.7749   $235.77   $235.75   $235.80  
  7 purchase totals = $905.95       $982.3270   $982.33   $982.30   $982.50