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 $149.86   12.462%   $168.5356   $168.54   $168.55   $168.50  
  Purchase #2 $89.97   9.526%   $98.5405   $98.54   $98.55   $98.50  
  Purchase #3 $32.81   12.137%   $36.7921   $36.79   $36.80   $36.80  
  Purchase #4 $244.31   9.859%   $268.3965   $268.40   $268.40   $268.40  
  Purchase #5 $105.97   3.492%   $109.6705   $109.67   $109.65   $109.70  
  Purchase #6 $129.66   6.459%   $138.0347   $138.03   $138.05   $138.00  
  Purchase #7 $199.58   6.323%   $212.1994   $212.20   $212.20   $212.20  
  7 purchase totals = $952.16       $1,032.1693   $1,032.17   $1,032.20   $1,032.10