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 $138.72   10.661%   $153.5089   $153.51   $153.50   $153.50  
  Purchase #2 $156.33   4.459%   $163.3008   $163.30   $163.30   $163.30  
  Purchase #3 $216.99   12.552%   $244.2266   $244.23   $244.25   $244.20  
  Purchase #4 $119.98   7.578%   $129.0721   $129.07   $129.05   $129.10  
  Purchase #5 $223.80   11.236%   $248.9462   $248.95   $248.95   $248.90  
  Purchase #6 $250.26   5.261%   $263.4262   $263.43   $263.45   $263.40  
  Purchase #7 $217.85   8.322%   $235.9795   $235.98   $236.00   $236.00  
  7 purchase totals = $1,323.93       $1,438.4603   $1,438.47   $1,438.50   $1,438.40