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 $169.59   13.482%   $192.4541   $192.45   $192.45   $192.50  
  Purchase #2 $118.95   3.699%   $123.35   $123.35   $123.35   $123.40  
  Purchase #3 $155.69   13.508%   $176.7206   $176.72   $176.70   $176.70  
  Purchase #4 $188.38   4.494%   $196.8458   $196.85   $196.85   $196.80  
  Purchase #5 $24.94   12.578%   $28.077   $28.08   $28.10   $28.10  
  Purchase #6 $193.75   3.260%   $200.0663   $200.07   $200.05   $200.10  
  Purchase #7 $232.47   8.742%   $252.7925   $252.79   $252.80   $252.80  
  7 purchase totals = $1,083.77       $1,170.3063   $1,170.31   $1,170.30   $1,170.40