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 $52.27   9.424%   $57.1959   $57.20   $57.20   $57.20  
  Purchase #2 $57.97   4.503%   $60.5804   $60.58   $60.60   $60.60  
  Purchase #3 $146.99   9.255%   $160.5939   $160.59   $160.60   $160.60  
  Purchase #4 $110.65   3.547%   $114.5748   $114.57   $114.55   $114.60  
  Purchase #5 $55.96   4.123%   $58.2672   $58.27   $58.25   $58.30  
  Purchase #6 $192.61   6.513%   $205.1547   $205.15   $205.15   $205.20  
  Purchase #7 $155.74   8.492%   $168.9654   $168.97   $168.95   $169.00  
  7 purchase totals = $772.19       $825.3323   $825.33   $825.30   $825.50