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 $227.44   8.647%   $247.1067   $247.11   $247.10   $247.10  
  Purchase #2 $71.95   10.397%   $79.4306   $79.43   $79.45   $79.40  
  Purchase #3 $88.59   7.197%   $94.9658   $94.97   $94.95   $95.00  
  Purchase #4 $210.74   7.611%   $226.7794   $226.78   $226.80   $226.80  
  Purchase #5 $61.93   10.533%   $68.4531   $68.45   $68.45   $68.50  
  Purchase #6 $72.30   8.410%   $78.3804   $78.38   $78.40   $78.40  
  Purchase #7 $78.36   6.157%   $83.1846   $83.18   $83.20   $83.20  
  7 purchase totals = $811.31       $878.3006   $878.30   $878.35   $878.40