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 $75.26   4.620%   $78.737   $78.74   $78.75   $78.70  
  Purchase #2 $240.39   6.713%   $256.5274   $256.53   $256.55   $256.50  
  Purchase #3 $213.66   8.684%   $232.2142   $232.21   $232.20   $232.20  
  Purchase #4 $216.83   10.623%   $239.8639   $239.86   $239.85   $239.90  
  Purchase #5 $81.47   5.638%   $86.0633   $86.06   $86.05   $86.10  
  Purchase #6 $225.52   9.108%   $246.0604   $246.06   $246.05   $246.10  
  Purchase #7 $53.86   6.432%   $57.3243   $57.32   $57.30   $57.30  
  7 purchase totals = $1,106.99       $1,196.7905   $1,196.78   $1,196.75   $1,196.80