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 $49.41   8.240%   $53.4814   $53.48   $53.50   $53.50  
  Purchase #2 $138.99   6.731%   $148.3454   $148.35   $148.35   $148.30  
  Purchase #3 $204.40   7.309%   $219.3396   $219.34   $219.35   $219.30  
  Purchase #4 $193.55   11.155%   $215.1405   $215.14   $215.15   $215.10  
  Purchase #5 $166.81   9.670%   $182.9405   $182.94   $182.95   $182.90  
  Purchase #6 $211.43   4.532%   $221.012   $221.01   $221.00   $221.00  
  Purchase #7 $109.42   10.255%   $120.641   $120.64   $120.65   $120.60  
  7 purchase totals = $1,074.01       $1,160.9004   $1,160.90   $1,160.95   $1,160.70