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 $33.97   6.732%   $36.2569   $36.26   $36.25   $36.30  
  Purchase #2 $236.35   6.740%   $252.28   $252.28   $252.30   $252.30  
  Purchase #3 $54.38   4.197%   $56.6623   $56.66   $56.65   $56.70  
  Purchase #4 $240.45   8.315%   $260.4434   $260.44   $260.45   $260.40  
  Purchase #5 $250.63   13.265%   $283.8761   $283.88   $283.90   $283.90  
  Purchase #6 $23.48   6.691%   $25.051   $25.05   $25.05   $25.10  
  Purchase #7 $73.86   8.180%   $79.9017   $79.90   $79.90   $79.90  
  7 purchase totals = $913.12       $994.4714   $994.47   $994.50   $994.60