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 $93.67   5.753%   $99.0588   $99.06   $99.05   $99.10  
  Purchase #2 $174.95   5.745%   $185.0009   $185.00   $185.00   $185.00  
  Purchase #3 $226.86   10.716%   $251.1703   $251.17   $251.15   $251.20  
  Purchase #4 $137.53   5.665%   $145.3211   $145.32   $145.30   $145.30  
  Purchase #5 $60.72   4.273%   $63.3146   $63.31   $63.30   $63.30  
  Purchase #6 $40.87   8.170%   $44.2091   $44.21   $44.20   $44.20  
  Purchase #7 $26.26   9.734%   $28.8161   $28.82   $28.80   $28.80  
  7 purchase totals = $760.86       $816.8909   $816.89   $816.80   $816.90