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 $17.30   10.106%   $19.0483   $19.05   $19.05   $19.00  
  Purchase #2 $129.47   8.317%   $140.238   $140.24   $140.25   $140.20  
  Purchase #3 $175.95   11.688%   $196.515   $196.52   $196.50   $196.50  
  Purchase #4 $42.60   3.692%   $44.1728   $44.17   $44.15   $44.20  
  Purchase #5 $71.65   8.450%   $77.7044   $77.70   $77.70   $77.70  
  Purchase #6 $66.29   8.167%   $71.7039   $71.70   $71.70   $71.70  
  Purchase #7 $85.34   4.551%   $89.2238   $89.22   $89.20   $89.20  
  7 purchase totals = $588.60       $638.6062   $638.60   $638.55   $638.50