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 $61.58   6.809%   $65.773   $65.77   $65.75   $65.80  
  Purchase #2 $13.55   13.571%   $15.3889   $15.39   $15.40   $15.40  
  Purchase #3 $144.32   9.144%   $157.5166   $157.52   $157.50   $157.50  
  Purchase #4 $148.70   8.726%   $161.6756   $161.68   $161.70   $161.70  
  Purchase #5 $190.92   8.767%   $207.658   $207.66   $207.65   $207.70  
  Purchase #6 $208.46   9.787%   $228.862   $228.86   $228.85   $228.90  
  Purchase #7 $111.44   6.620%   $118.8173   $118.82   $118.80   $118.80  
  7 purchase totals = $878.97       $955.6914   $955.70   $955.65   $955.80