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 $70.36   10.718%   $77.9012   $77.90   $77.90   $77.90  
  Purchase #2 $88.94   4.673%   $93.0962   $93.10   $93.10   $93.10  
  Purchase #3 $84.97   9.105%   $92.7065   $92.71   $92.70   $92.70  
  Purchase #4 $86.98   11.317%   $96.8235   $96.82   $96.80   $96.80  
  Purchase #5 $202.66   10.833%   $224.6142   $224.61   $224.60   $224.60  
  Purchase #6 $235.75   4.200%   $245.6515   $245.65   $245.65   $245.70  
  Purchase #7 $191.29   5.438%   $201.6924   $201.69   $201.70   $201.70  
  7 purchase totals = $960.95       $1,032.4855   $1,032.48   $1,032.45   $1,032.50