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 $119.33   11.717%   $133.3119   $133.31   $133.30   $133.30  
  Purchase #2 $131.48   12.204%   $147.5258   $147.53   $147.55   $147.50  
  Purchase #3 $13.88   7.699%   $14.9486   $14.95   $14.95   $14.90  
  Purchase #4 $249.98   8.482%   $271.1833   $271.18   $271.20   $271.20  
  Purchase #5 $35.38   7.255%   $37.9468   $37.95   $37.95   $37.90  
  Purchase #6 $215.39   12.278%   $241.8356   $241.84   $241.85   $241.80  
  Purchase #7 $24.74   9.341%   $27.051   $27.05   $27.05   $27.10  
  7 purchase totals = $790.18       $873.8030   $873.81   $873.85   $873.70