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 $69.85   10.787%   $77.3847   $77.38   $77.40   $77.40  
  Purchase #2 $210.52   11.139%   $233.9698   $233.97   $233.95   $234.00  
  Purchase #3 $24.87   8.604%   $27.0098   $27.01   $27.00   $27.00  
  Purchase #4 $120.77   12.189%   $135.4907   $135.49   $135.50   $135.50  
  Purchase #5 $47.76   9.213%   $52.1601   $52.16   $52.15   $52.20  
  Purchase #6 $192.89   8.628%   $209.5325   $209.53   $209.55   $209.50  
  Purchase #7 $158.36   10.615%   $175.1699   $175.17   $175.15   $175.20  
  7 purchase totals = $825.02       $910.7175   $910.71   $910.70   $910.80