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 $49.47   7.538%   $53.199   $53.20   $53.20   $53.20  
  Purchase #2 $81.41   5.608%   $85.9755   $85.98   $86.00   $86.00  
  Purchase #3 $178.94   12.866%   $201.9624   $201.96   $201.95   $202.00  
  Purchase #4 $101.56   7.562%   $109.24   $109.24   $109.25   $109.20  
  Purchase #5 $242.72   3.124%   $250.3026   $250.30   $250.30   $250.30  
  Purchase #6 $95.82   7.717%   $103.2144   $103.21   $103.20   $103.20  
  Purchase #7 $124.40   4.157%   $129.5713   $129.57   $129.55   $129.60  
  7 purchase totals = $874.32       $933.4652   $933.46   $933.45   $933.50