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 $155.25   8.198%   $167.9774   $167.98   $168.00   $168.00  
  Purchase #2 $194.54   4.184%   $202.6796   $202.68   $202.70   $202.70  
  Purchase #3 $10.64   8.693%   $11.5649   $11.56   $11.55   $11.60  
  Purchase #4 $114.68   5.345%   $120.8096   $120.81   $120.80   $120.80  
  Purchase #5 $89.72   4.851%   $94.0723   $94.07   $94.05   $94.10  
  Purchase #6 $213.69   3.270%   $220.6777   $220.68   $220.70   $220.70  
  Purchase #7 $246.25   5.287%   $259.2692   $259.27   $259.25   $259.30  
  7 purchase totals = $1,024.77       $1,077.0507   $1,077.05   $1,077.05   $1,077.20