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 $58.74   5.849%   $62.1757   $62.18   $62.20   $62.20  
  Purchase #2 $205.60   9.620%   $225.3787   $225.38   $225.40   $225.40  
  Purchase #3 $138.86   13.661%   $157.8297   $157.83   $157.85   $157.80  
  Purchase #4 $246.99   5.115%   $259.6235   $259.62   $259.60   $259.60  
  Purchase #5 $35.86   7.166%   $38.4297   $38.43   $38.45   $38.40  
  Purchase #6 $180.46   8.487%   $195.7756   $195.78   $195.80   $195.80  
  Purchase #7 $75.70   13.557%   $85.9626   $85.96   $85.95   $86.00  
  7 purchase totals = $942.21       $1,025.1755   $1,025.18   $1,025.25   $1,025.20