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 $154.79   10.173%   $170.5368   $170.54   $170.55   $170.50  
  Purchase #2 $221.56   9.660%   $242.9627   $242.96   $242.95   $243.00  
  Purchase #3 $85.70   6.135%   $90.9577   $90.96   $90.95   $91.00  
  Purchase #4 $181.38   6.705%   $193.5415   $193.54   $193.55   $193.50  
  Purchase #5 $84.75   7.281%   $90.9206   $90.92   $90.90   $90.90  
  Purchase #6 $232.92   6.723%   $248.5792   $248.58   $248.60   $248.60  
  Purchase #7 $149.37   11.397%   $166.3937   $166.39   $166.40   $166.40  
  7 purchase totals = $1,110.47       $1,203.8922   $1,203.89   $1,203.90   $1,203.90