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 $59.81   6.398%   $63.6366   $63.64   $63.65   $63.60  
  Purchase #2 $183.73   11.667%   $205.1658   $205.17   $205.15   $205.20  
  Purchase #3 $121.58   8.824%   $132.3082   $132.31   $132.30   $132.30  
  Purchase #4 $81.86   13.449%   $92.8694   $92.87   $92.85   $92.90  
  Purchase #5 $227.31   7.636%   $244.6674   $244.67   $244.65   $244.70  
  Purchase #6 $83.58   7.788%   $90.0892   $90.09   $90.10   $90.10  
  Purchase #7 $197.78   7.418%   $212.4513   $212.45   $212.45   $212.50  
  7 purchase totals = $955.65       $1,041.1879   $1,041.20   $1,041.15   $1,041.30