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 $52.59   12.811%   $59.3273   $59.33   $59.35   $59.30  
  Purchase #2 $239.70   5.174%   $252.1021   $252.10   $252.10   $252.10  
  Purchase #3 $167.50   6.532%   $178.4411   $178.44   $178.45   $178.40  
  Purchase #4 $147.47   10.718%   $163.2758   $163.28   $163.30   $163.30  
  Purchase #5 $8.65   10.774%   $9.582   $9.58   $9.60   $9.60  
  Purchase #6 $234.37   8.204%   $253.5977   $253.60   $253.60   $253.60  
  Purchase #7 $119.71   11.218%   $133.1391   $133.14   $133.15   $133.10  
  7 purchase totals = $969.99       $1,049.4651   $1,049.47   $1,049.55   $1,049.40