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 $84.28   12.179%   $94.5445   $94.54   $94.55   $94.50  
  Purchase #2 $207.38   8.580%   $225.1732   $225.17   $225.15   $225.20  
  Purchase #3 $230.46   13.817%   $262.3027   $262.30   $262.30   $262.30  
  Purchase #4 $48.46   6.161%   $51.4456   $51.45   $51.45   $51.40  
  Purchase #5 $179.28   12.284%   $201.3028   $201.30   $201.30   $201.30  
  Purchase #6 $229.93   13.373%   $260.6785   $260.68   $260.70   $260.70  
  Purchase #7 $241.95   11.770%   $270.4275   $270.43   $270.45   $270.40  
  7 purchase totals = $1,221.74       $1,365.8748   $1,365.87   $1,365.90   $1,365.80