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 $82.66   12.273%   $92.8049   $92.80   $92.80   $92.80  
  Purchase #2 $236.88   5.767%   $250.5409   $250.54   $250.55   $250.50  
  Purchase #3 $162.94   6.816%   $174.046   $174.05   $174.05   $174.00  
  Purchase #4 $240.82   5.676%   $254.4889   $254.49   $254.50   $254.50  
  Purchase #5 $31.91   8.212%   $34.5304   $34.53   $34.55   $34.50  
  Purchase #6 $168.49   5.629%   $177.9743   $177.97   $177.95   $178.00  
  Purchase #7 $196.25   3.192%   $202.5143   $202.51   $202.50   $202.50  
  7 purchase totals = $1,119.95       $1,186.8997   $1,186.89   $1,186.90   $1,186.80