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 $147.41   10.198%   $162.4429   $162.44   $162.45   $162.40  
  Purchase #2 $136.81   5.715%   $144.6287   $144.63   $144.65   $144.60  
  Purchase #3 $214.58   12.540%   $241.4883   $241.49   $241.50   $241.50  
  Purchase #4 $182.77   12.690%   $205.9635   $205.96   $205.95   $206.00  
  Purchase #5 $93.51   8.567%   $101.521   $101.52   $101.50   $101.50  
  Purchase #6 $190.39   11.180%   $211.6756   $211.68   $211.70   $211.70  
  Purchase #7 $50.82   8.427%   $55.1026   $55.10   $55.10   $55.10  
  7 purchase totals = $1,016.29       $1,122.8226   $1,122.82   $1,122.85   $1,122.80