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 $184.52   11.407%   $205.5682   $205.57   $205.55   $205.60  
  Purchase #2 $44.51   4.676%   $46.5913   $46.59   $46.60   $46.60  
  Purchase #3 $98.62   3.135%   $101.7117   $101.71   $101.70   $101.70  
  Purchase #4 $202.77   12.174%   $227.4552   $227.46   $227.45   $227.50  
  Purchase #5 $89.93   5.862%   $95.2017   $95.20   $95.20   $95.20  
  Purchase #6 $214.70   11.157%   $238.6541   $238.65   $238.65   $238.70  
  Purchase #7 $101.37   6.779%   $108.2419   $108.24   $108.25   $108.20  
  7 purchase totals = $936.42       $1,023.4241   $1,023.42   $1,023.40   $1,023.50