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 $91.66   4.457%   $95.7453   $95.75   $95.75   $95.70  
  Purchase #2 $20.64   6.539%   $21.9896   $21.99   $22.00   $22.00  
  Purchase #3 $50.69   6.695%   $54.0837   $54.08   $54.10   $54.10  
  Purchase #4 $244.80   11.844%   $273.7941   $273.79   $273.80   $273.80  
  Purchase #5 $240.41   4.754%   $251.8391   $251.84   $251.85   $251.80  
  Purchase #6 $176.32   3.606%   $182.6781   $182.68   $182.70   $182.70  
  Purchase #7 $101.85   13.721%   $115.8248   $115.82   $115.80   $115.80  
  7 purchase totals = $926.37       $995.9547   $995.95   $996.00   $995.90