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 $205.66   10.520%   $227.2954   $227.30   $227.30   $227.30  
  Purchase #2 $201.49   12.127%   $225.9247   $225.92   $225.90   $225.90  
  Purchase #3 $196.72   13.125%   $222.5395   $222.54   $222.55   $222.50  
  Purchase #4 $55.42   11.847%   $61.9856   $61.99   $62.00   $62.00  
  Purchase #5 $235.28   9.120%   $256.7375   $256.74   $256.75   $256.70  
  Purchase #6 $59.85   6.620%   $63.8121   $63.81   $63.80   $63.80  
  Purchase #7 $118.37   12.606%   $133.2917   $133.29   $133.30   $133.30  
  7 purchase totals = $1,072.79       $1,191.5865   $1,191.59   $1,191.60   $1,191.50