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 $183.50   4.413%   $191.5979   $191.60   $191.60   $191.60  
  Purchase #2 $201.87   11.708%   $225.5049   $225.50   $225.50   $225.50  
  Purchase #3 $97.30   5.348%   $102.5036   $102.50   $102.50   $102.50  
  Purchase #4 $83.75   6.160%   $88.909   $88.91   $88.90   $88.90  
  Purchase #5 $118.64   13.686%   $134.8771   $134.88   $134.90   $134.90  
  Purchase #6 $180.59   11.615%   $201.5655   $201.57   $201.55   $201.60  
  Purchase #7 $56.39   9.150%   $61.5497   $61.55   $61.55   $61.50  
  7 purchase totals = $922.04       $1,006.5077   $1,006.51   $1,006.50   $1,006.50