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 $202.57   3.162%   $208.9753   $208.98   $209.00   $209.00  
  Purchase #2 $179.25   8.205%   $193.9575   $193.96   $193.95   $194.00  
  Purchase #3 $49.45   12.703%   $55.7316   $55.73   $55.75   $55.70  
  Purchase #4 $201.86   8.351%   $218.7173   $218.72   $218.70   $218.70  
  Purchase #5 $135.31   9.823%   $148.6015   $148.60   $148.60   $148.60  
  Purchase #6 $42.99   8.328%   $46.5702   $46.57   $46.55   $46.60  
  Purchase #7 $123.52   11.438%   $137.6482   $137.65   $137.65   $137.60  
  7 purchase totals = $934.95       $1,010.2016   $1,010.21   $1,010.20   $1,010.20