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 $50.79   5.752%   $53.7114   $53.71   $53.70   $53.70  
  Purchase #2 $220.77   12.650%   $248.6974   $248.70   $248.70   $248.70  
  Purchase #3 $189.27   6.751%   $202.0476   $202.05   $202.05   $202.00  
  Purchase #4 $21.94   13.498%   $24.9015   $24.90   $24.90   $24.90  
  Purchase #5 $250.31   9.467%   $274.0068   $274.01   $274.00   $274.00  
  Purchase #6 $162.69   5.410%   $171.4915   $171.49   $171.50   $171.50  
  Purchase #7 $77.83   9.706%   $85.3842   $85.38   $85.40   $85.40  
  7 purchase totals = $973.60       $1,060.2404   $1,060.24   $1,060.25   $1,060.20