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 $138.93   9.785%   $152.5243   $152.52   $152.50   $152.50  
  Purchase #2 $182.95   8.581%   $198.6489   $198.65   $198.65   $198.60  
  Purchase #3 $179.46   6.657%   $191.4067   $191.41   $191.40   $191.40  
  Purchase #4 $186.81   9.227%   $204.047   $204.05   $204.05   $204.00  
  Purchase #5 $58.43   7.669%   $62.911   $62.91   $62.90   $62.90  
  Purchase #6 $122.62   9.846%   $134.6932   $134.69   $134.70   $134.70  
  Purchase #7 $94.84   13.576%   $107.7155   $107.72   $107.70   $107.70  
  7 purchase totals = $964.04       $1,051.9466   $1,051.95   $1,051.90   $1,051.80