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 $124.90   7.720%   $134.5423   $134.54   $134.55   $134.50  
  Purchase #2 $175.57   5.240%   $184.7699   $184.77   $184.75   $184.80  
  Purchase #3 $79.57   6.222%   $84.5208   $84.52   $84.50   $84.50  
  Purchase #4 $203.82   8.580%   $221.3078   $221.31   $221.30   $221.30  
  Purchase #5 $15.93   12.142%   $17.8642   $17.86   $17.85   $17.90  
  Purchase #6 $220.26   12.589%   $247.9885   $247.99   $248.00   $248.00  
  Purchase #7 $105.70   13.126%   $119.5742   $119.57   $119.55   $119.60  
  7 purchase totals = $925.75       $1,010.5677   $1,010.56   $1,010.50   $1,010.60